net: hns: remove redundant variables 'max_frm' and 'tmp_mac_key'

Variables 'max_frm' and 'tmp_mac_key' are being assigned,
but are never used,hence they are redundant and can be removed.

fix fllowing warning:

drivers/net/ethernet/hisilicon/hns/hns_dsaf_mac.c:461:6: warning: variable 'max_frm' set but not used [-Wunused-but-set-variable]
drivers/net/ethernet/hisilicon/hns/hns_dsaf_main.c:1685:31: warning: variable 'tmp_mac_key' set but not used [-Wunused-but-set-variable]
drivers/net/ethernet/hisilicon/hns/hns_dsaf_main.c:1855:41: warning: variable 'tmp_mac_key' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>