drivers/net/ethernet: clean up unused assignments

As part of the W=1 compliation series, these lines all created
warnings about unused variables that were assigned a value. Most
of them are from register reads, but some are just picking up
a return value from a function and never doing anything with it.

Fixed warnings:
.../ethernet/brocade/bna/bnad.c:3280:6: warning: variable ‘rx_count’ set but not used [-Wunused-but-set-variable]
.../ethernet/brocade/bna/bnad.c:3280:6: warning: variable ‘rx_count’ set but not used [-Wunused-but-set-variable]
.../ethernet/cortina/gemini.c:512:6: warning: variable ‘val’ set but not used [-Wunused-but-set-variable]
.../ethernet/cortina/gemini.c:2110:21: warning: variable ‘config0’ set but not used [-Wunused-but-set-variable]
.../ethernet/cavium/liquidio/octeon_device.c:1327:6: warning: variable ‘val32’ set but not used [-Wunused-but-set-variable]
.../ethernet/cavium/liquidio/octeon_device.c:1358:6: warning: variable ‘val32’ set but not used [-Wunused-but-set-variable]
.../ethernet/dec/tulip/media.c:322:8: warning: variable ‘setup’ set but not used [-Wunused-but-set-variable]
.../ethernet/dec/tulip/de4x5.c:4928:13: warning: variable ‘r3’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:1652:7: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:1652:7: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:1652:7: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:1652:7: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:4981:6: warning: variable ‘rx_status’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:6510:6: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
.../ethernet/micrel/ksz884x.c:6087: warning: cannot understand function prototype: 'struct hw_regs '
.../ethernet/microchip/lan743x_main.c:161:6: warning: variable ‘int_en’ set but not used [-Wunused-but-set-variable]
.../ethernet/microchip/lan743x_main.c:1702:6: warning: variable ‘int_sts’ set but not used [-Wunused-but-set-variable]
.../ethernet/microchip/lan743x_main.c:3041:6: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]
.../ethernet/natsemi/ns83820.c:603:6: warning: variable ‘tbisr’ set but not used [-Wunused-but-set-variable]
.../ethernet/natsemi/ns83820.c:1207:11: warning: variable ‘tanar’ set but not used [-Wunused-but-set-variable]
.../ethernet/marvell/mvneta.c:754:6: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
.../ethernet/neterion/vxge/vxge-traffic.c:33:6: warning: variable ‘val64’ set but not used [-Wunused-but-set-variable]
.../ethernet/neterion/vxge/vxge-traffic.c:160:6: warning: variable ‘val64’ set but not used [-Wunused-but-set-variable]
.../ethernet/neterion/vxge/vxge-traffic.c:490:6: warning: variable ‘val32’ set but not used [-Wunused-but-set-variable]
.../ethernet/neterion/vxge/vxge-traffic.c:2378:6: warning: variable ‘val64’ set but not used [-Wunused-but-set-variable]
.../ethernet/packetengines/yellowfin.c:1063:18: warning: variable ‘yf_size’ set but not used [-Wunused-but-set-variable]
.../ethernet/realtek/8139cp.c:1242:6: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
.../ethernet/mellanox/mlx4/en_tx.c:858:6: warning: variable ‘ring_cons’ set but not used [-Wunused-but-set-variable]
.../ethernet/sis/sis900.c:792:6: warning: variable ‘status’ set but not used [-Wunused-but-set-variable]
.../ethernet/sfc/falcon/farch.c:878:11: warning: variable ‘rx_ev_pkt_type’ set but not used [-Wunused-but-set-variable]
.../ethernet/sfc/falcon/farch.c:877:23: warning: variable ‘rx_ev_mcast_pkt’ set but not used [-Wunused-but-set-variable]
.../ethernet/sfc/falcon/farch.c:877:7: warning: variable ‘rx_ev_hdr_type’ set but not used [-Wunused-but-set-variable]
.../ethernet/sfc/falcon/farch.c:876:7: warning: variable ‘rx_ev_other_err’ set but not used [-Wunused-but-set-variable]
.../ethernet/sfc/falcon/farch.c:1646:21: warning: variable ‘buftbl_min’ set but not used [-Wunused-but-set-variable]
.../ethernet/sfc/falcon/farch.c:2535:32: warning: variable ‘spec’ set but not used [-Wunused-but-set-variable]
.../ethernet/via/via-velocity.c:880:6: warning: variable ‘curr_status’ set but not used [-Wunused-but-set-variable]
.../ethernet/ti/tlan.c:656:6: warning: variable ‘rc’ set but not used [-Wunused-but-set-variable]
.../ethernet/ti/davinci_emac.c:1230:6: warning: variable ‘num_tx_pkts’ set but not used [-Wunused-but-set-variable]
.../ethernet/synopsys/dwc-xlgmac-common.c:516:8: warning: variable ‘str’ set but not used [-Wunused-but-set-variable]
.../ethernet/ti/cpsw_new.c:1662:22: warning: variable ‘priv’ set but not used [-Wunused-but-set-variable]

The register reads should be OK, because the current
implementation of readl and friends will always execute even
without an lvalue.

When it makes sense, just remove the lvalue assignment and the
local. Other times, just remove the offending code, and
occasionally, just mark the variable as maybe unused since it
could be used in an ifdef or debug scenario.

Only compile tested with W=1.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>