meta-wayland-single-pixel-buffer.c: Use correct cogl ref function,

fix leak.

- In muffin, cogl objects aren't GObjects.
- While testing, the extra refs leaked according to valgrind, so
  unref first.

Author: mtwebster

src/wayland/meta-wayland-single-pixel-buffer.c

@@ -122,7 +122,8 @@ meta_wayland_single_pixel_buffer_attach (MetaWaylandBuffer  *buffer,
 
   if (buffer->single_pixel.texture)
     {
-      *texture = g_object_ref (buffer->single_pixel.texture);
+      cogl_clear_object (texture);
+      *texture = cogl_object_ref (buffer->single_pixel.texture);
       return TRUE;
     }