MetaRendererView: Fix GObject parent

Set ClutterStageViewCogl as parent of MetaRendererView, since that is
the actual parent.

https://bugzilla.gnome.org/show_bug.cgi?id=768976

src/backends/meta-renderer-view.c

@@ -35,7 +35,7 @@ static GParamSpec *obj_props[PROP_LAST];
 
 struct _MetaRendererView
 {
-  ClutterStageView parent;
+  ClutterStageViewCogl parent;
 
   MetaMonitorInfo *monitor_info;
 };