[gnome-control-center] thunderbolt: Fix compile warning

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

commit 65cb7e98d11c4d08a81531590fe53314a59eee5d
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Nov 6 11:39:48 2018 +1300

    thunderbolt: Fix compile warning

 panels/thunderbolt/cc-bolt-panel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/panels/thunderbolt/cc-bolt-panel.c b/panels/thunderbolt/cc-bolt-panel.c
index a4face5b3..b6a5cd607 100644
--- a/panels/thunderbolt/cc-bolt-panel.c
+++ b/panels/thunderbolt/cc-bolt-panel.c
@@ -862,7 +862,7 @@ cc_bolt_panel_dispose (GObject *object)
   g_cancellable_cancel (panel->cancel);
 
   /* Must be destroyed in dispose, not finalize. */
-  g_clear_pointer (&panel->device_dialog, gtk_widget_destroy);
+  g_clear_pointer ((GtkWidget **) &panel->device_dialog, gtk_widget_destroy);
 
   G_OBJECT_CLASS (cc_bolt_panel_parent_class)->dispose (object);
 }