liquidio CN23XX: Remove set but not used variable 'ring_flag'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/cavium/liquidio/cn23xx_vf_device.c: In function 'cn23xx_setup_octeon_vf_device':
drivers/net/ethernet/cavium/liquidio/cn23xx_vf_device.c:619:20: warning:
 variable 'ring_flag' set but not used [-Wunused-but-set-variable]

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