IB/mlx4_ib: Adapt code to use caps.num_ports instead of a constant

Some code in the mlx4 IB driver stack assumed MLX4_MAX_PORTS ports.

Instead, we should only loop until the number of actual ports in i
the device, which is stored in dev->caps.num_ports.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>