[metacity] bell: fix build warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 707f1dad098f8fb6a4d63d00c86770f6b96d522f
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Sep 20 05:04:17 2015 +0300

    bell: fix build warning

 src/core/bell.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/core/bell.c b/src/core/bell.c
index 3fa0294..3203331 100644
--- a/src/core/bell.c
+++ b/src/core/bell.c
@@ -269,6 +269,8 @@ bell_visual_notify (MetaDisplay *display,
     case G_DESKTOP_VISUAL_BELL_FRAME_FLASH:
       bell_flash_frame (display, xkb_ev); /* does nothing yet */
       break;
+    default:
+      break;
     }
 }