RDMA/nes: Fix for crash when registering zero length MR for CQ

commit 7d9c199a55200c9b9fcad08e150470d02fb385be upstream.

Signed-off-by: Tatyana Nikolova <Tatyana.E.Nikolova@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>