RDMA/hns: Fix return in hns_roce_rereg_user_mr()

If re-registering an MR in hns_roce_rereg_user_mr(), we should return NULL
instead of passing 0 to ERR_PTR for clarity.

Fixes: 4e9fc1da ("RDMA/hns: Optimize the MR registration process")
Link: https://lore.kernel.org/r/20210804125939.20516-1-yuehaibing@huawei.comSigned-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/hns/hns_roce_mr.c

@@ -352,7 +352,9 @@ struct ib_mr *hns_roce_rereg_user_mr(struct ib_mr *ibmr, int flags, u64 start,
 free_cmd_mbox:
 	hns_roce_free_cmd_mailbox(hr_dev, mailbox);
 
-	return ERR_PTR(ret);
+	if (ret)
+		return ERR_PTR(ret);
+	return NULL;
 }
 
 int hns_roce_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)