RDMA/iw_cxgb4: Report correct port speed/width

Query speed/width from corresponding netdev.

Link: https://lore.kernel.org/r/1572001022-4533-1-git-send-email-bharat@chelsio.com
Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>