RDMA/efa: Remove umem check on dereg MR flow

EFA driver is not a kverbs provider, the check for MR umem is redundant.

Link: https://lore.kernel.org/r/20190826115350.21718-2-galpress@amazon.com


Reviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>