[mutter] clutter/offscreen-effect: Use memory management helpers more

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 29cdc3565411c868697dfcc9264d996a034f33f4
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Oct 14 21:14:56 2020 +0200

    clutter/offscreen-effect: Use memory management helpers more
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1496

 clutter/clutter/clutter-offscreen-effect.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/clutter/clutter/clutter-offscreen-effect.c b/clutter/clutter/clutter-offscreen-effect.c
index 6315caa730..cfb0ddc955 100644
--- a/clutter/clutter/clutter-offscreen-effect.c
+++ b/clutter/clutter/clutter-offscreen-effect.c
@@ -240,8 +240,7 @@ update_fbo (ClutterEffect *effect,
                  error->message);
 
       g_object_unref (offscreen);
-      cogl_object_unref (priv->pipeline);
-      priv->pipeline = NULL;
+      cogl_clear_object (&priv->pipeline);
 
       priv->target_width = 0;
       priv->target_height = 0;