RDMA/providers: Remove pointless functions

The rdma core is taking care of return the right error code when the
rdma device callbacks aren't supported.

Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Acked-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>