net/mlx4_en: Hardware accelerated 802.1ad works only on the first port

Fix mistakenly used, hard coded, port number in get_phv_bit()

Fixes: 77fc29c4 ("net/mlx4_core: Preparations for 802.1ad VLAN support")
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>