[metacity] prefs: fix cast-function-type warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit fd5c295d3d51e0a25a298187e9968c8c0c42171b
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Sep 2 13:57:40 2018 +0300

    prefs: fix cast-function-type warning

 src/core/prefs.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/src/core/prefs.c b/src/core/prefs.c
index 7ce0028c..613e35b7 100644
--- a/src/core/prefs.c
+++ b/src/core/prefs.c
@@ -1305,8 +1305,7 @@ update_binding (MetaKeyPref *binding,
   /* Okay, so, we're about to provide a new list of key combos for this
    * action. Delete any pre-existing list.
    */
-  g_slist_foreach (binding->bindings, (GFunc) g_free, NULL);
-  g_slist_free (binding->bindings);
+  g_slist_free_full (binding->bindings, g_free);
   binding->bindings = NULL;
 
   for (i = 0; strokes && strokes[i]; i++)