RDMA/hns: Fix the bug with NULL pointer

When the last QP of eight QPs is not exist in
hns_roce_v1_mr_free_work_fn function, the
print for qpn of hr_qp may introduce a
calltrace for NULL pointer.
Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/hns/hns_roce_hw_v1.c

@@ -1037,7 +1037,7 @@ static void hns_roce_v1_mr_free_work_fn(struct work_struct *work)
 
 	do {
 		ret = hns_roce_v1_poll_cq(&mr_free_cq->ib_cq, ne, wc);
-		if (ret < 0) {
+		if (ret < 0 && hr_qp) {
 			dev_err(dev,
 			   "(qp:0x%lx) starts, Poll cqe failed(%d) for mr 0x%x free! Remain %d cqe\n",
 			   hr_qp->qpn, ret, hr_mr->key, ne);