RDMA/rxe: Recheck the MR in when generating a READ reply

RDMA/rxe: Recheck the MR in when generating a READ reply

The rping benchmark fails on long runs. The root cause of this failure has
been traced to a failure to compute a nonzero value of mr in rare
situations.

Fix this failure by correctly handling the computation of mr in
read_reply() in rxe_resp.c in the replay flow.

Fixes: 6749bb9c6268 ("RDMA/rxe: Replace mr by rkey in responder resources")
Link: https://lore.kernel.org/r/20220418174103.3040-1-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>