RDMA/ipoib: Fix return code from ipoib_cm_dev_init

The proper return code is -EOPNOTSUPP and not -ENOSYS when the function
isn't supported, also make sure to return the right error code
from ipoib_transport_dev_init() when ipoib_cm_dev_init() is supported.

Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>