RDMA/rxe: Remove duplicate entries in struct rxe_mr

RDMA/rxe: Remove duplicate entries in struct rxe_mr

Struct rxe_mem had pd, lkey and rkey values both in itself and in the
struct ib_mr which is also included in rxe_mem.

Delete these entries and replace references with the ones in ibmr.Add
mr_pd, mr_lkey and mr_rkey macros which extract these values from mr.

Link: https://lore.kernel.org/r/20201008212818.265303-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>