net: cortina: Remove set but not used variable

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

drivers/net/ethernet/cortina/gemini.c: In function gmac_get_ringparam:
drivers/net/ethernet/cortina/gemini.c:2125:21: warning: variable ‘config0’ set but not used [-Wunused-but-set-variable]

drivers/net/ethernet/cortina/gemini.c: In function gmac_init:
drivers/net/ethernet/cortina/gemini.c:512:6: warning: variable ‘val’ set but not used [-Wunused-but-set-variable]

these variable is never used, so remove it.

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>