[gnome-control-center] color: Fix compile warning on g_clear_pointer

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

commit 8ecdd32971679e03f0eddce2db8dd105bc016056
Author: Robert Ancell <robert ancell canonical com>
Date:   Thu Feb 7 11:22:11 2019 +1300

    color: Fix compile warning on g_clear_pointer

 panels/color/cc-color-calibrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/panels/color/cc-color-calibrate.c b/panels/color/cc-color-calibrate.c
index 3861213b2..4b96df3ea 100644
--- a/panels/color/cc-color-calibrate.c
+++ b/panels/color/cc-color-calibrate.c
@@ -990,7 +990,7 @@ cc_color_calibrate_finalize (GObject *object)
 {
   CcColorCalibrate *calibrate = CC_COLOR_CALIBRATE (object);
 
-  g_clear_pointer (&calibrate->window, gtk_widget_destroy);
+  g_clear_pointer ((GtkWidget **)&calibrate->window, gtk_widget_destroy);
   g_clear_object (&calibrate->builder);
   g_clear_object (&calibrate->device);
   g_clear_object (&calibrate->proxy_helper);