Fixes the following sparse warning:

drivers/net/ethernet/sfc/efx.c:2337:5: warning:
 symbol 'efx_get_phys_port_id' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>