net/mlx4_core: Fix call to __mlx4_unregister_mac

In function mlx4_master_deactivate_admin_state() __mlx4_unregister_mac was
called using the MAC index. It should be called with the value of the MAC itself.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>