waylandsink: Commit the parent after creating subsurface

We should commit the parent to activate new subsurface, this is
documented in the protocol.

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>

ext/wayland/wlwindow.c

@@ -350,6 +350,8 @@ gst_wl_window_new_in_surface (GstWlDisplay * display,
       window->area_surface, parent);
   wl_subsurface_set_desync (window->area_subsurface);
 
+  wl_surface_commit (parent);
+
   return window;
 }