RDMA/efa: Remove .create_ah callback assignment

Drivers now expose two callbacks for address handle creation, one for
uverbs and one for kverbs. EFA only supports uverbs so the .create_ah
assignment can be removed. Fix the core code caller to check the proper
function pointer.

Link: https://lore.kernel.org/r/20201115103404.48829-3-galpress@amazon.com


Signed-off-by: Gal Pressman <galpress@amazon.com>
Acked-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>