RDMA/hns: Fixup bug of null point checking

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

In addition to the error value,
we should also check the ib_umem_get return null pointer.
Signed-off-by: NLang Cheng <chenglang@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/infiniband/hw/hns/hns_roce_db.c

@@ -31,7 +31,10 @@ int hns_roce_db_map_user(struct hns_roce_ucontext *context, unsigned long virt,
 	page->user_virt = (virt & PAGE_MASK);
 	page->umem = ib_umem_get(&context->ibucontext, virt & PAGE_MASK,
 				 PAGE_SIZE, 0, 0);
-	if (IS_ERR(page->umem)) {
+	if (IS_ERR_OR_NULL(page->umem)) {
+		if (!page->umem)
+			ret = -EINVAL;
+		else
 			ret = PTR_ERR(page->umem);
 		kfree(page);
 		goto out;