RDMA/hns: Fix the bug with rq sge

When received multiply rq sge, it should tag the
invalid lkey for the last non-zero length sge
when have some sges' length are zero. This patch
fixes it.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>