net/mlx4_en: Fix the return value of a failure in VLAN VID add/kill

Modify mlx4_en_vlan_rx_[add/kill]_vid to return error value in case of
failure.

Fixes: 8e586137

 ('net: make vlan ndo_vlan_rx_[add/kill]_vid return error value')
Signed-off-by: Kamal Heib <kamalh@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>