pipeline: Plug a leak of GLists

_cogl_pipeline_get_layers() allocates a list on the pipeline to be able
to get the pointer valid as long as possible and store that list in the
pipeline object.

You need to free that list when freeing the pipeline.

Signed-off-by: Robert Bragg <robert@linux.intel.com>

cogl/cogl-pipeline.c

@@ -562,6 +562,8 @@ _cogl_pipeline_free (CoglPipeline *pipeline)
       g_list_free (pipeline->layer_differences);
     }
 
+  g_list_free (pipeline->deprecated_get_layers_list);
+
   g_slice_free (CoglPipeline, pipeline);
 }