sfc: avoid an unused-variable warning

'nic_data' is no longer used outside of the #ifdef block
in efx_ef10_set_mac_address:

drivers/net/ethernet/sfc/ef10.c:3231:28: error: unused variable 'nic_data' [-Werror,-Wunused-variable]
        struct efx_ef10_nic_data *nic_data = efx->nic_data;

Move the variable into a local scope.

Fixes: dfcabb07 ("sfc: move vport_id to struct efx_nic")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>