ibmvnic: remove set but not used variable 'netdev'

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

drivers/net/ethernet/ibm/ibmvnic.c: In function '__ibmvnic_reset':
drivers/net/ethernet/ibm/ibmvnic.c:1971:21: warning: variable 'netdev' set but not used [-Wunused-but-set-variable]

It's never used since introduction in
commit ed651a10 ("ibmvnic: Updated reset handling")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>