RDMA/core: Remove err in iw_query_port

Since we can return device->ops.query_port directly, so no need to keep
those lines.

Link: https://lore.kernel.org/r/20200109134043.15568-1-guoqing.jiang@cloud.ionos.com
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>