RDMA/mlx5: Use the proper number of ports

The cited commit allowed the driver to operate over HCAs that have
4 physical ports. Use the number of ports of the RDMA device in the for
loop instead of using the struct size.

Fixes: 4cd14d44

 ("net/mlx5: Support devices with more than 2 ports")
Link: https://lore.kernel.org/r/a54a56c2ede16044a29d119209b35189c662ac72.1659944855.git.leonro@nvidia.com
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>