IB/mlx4: Use port iterator and validation APIs

Use IB core provided routine to check if the port is valid or not and to
iterate over IB ports.

Link: https://lore.kernel.org/r/20210127150010.1876121-10-leon@kernel.org


Signed-off-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>