block: Propagate error in bdrv_open_backing_file

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index a77e8a0..e538084 100644
--- a/block.c
+++ b/block.c
@@ -2030,6 +2030,7 @@
     bdrv_set_backing_hd(bs, backing_hd, &local_err);
     bdrv_unref(backing_hd);
     if (local_err) {
+        error_propagate(errp, local_err);
         ret = -EINVAL;
         goto free_exit;
     }