RDMA/cma: Use RDMA device port iterator

Use RDMA device port iterator to avoid open coding.

Link: https://lore.kernel.org/r/20200126142652.104803-4-leon@kernel.org


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