[mutter/wayland] window: Fix a compiler warning

[Jasper St. Pierre <jstpierre src gnome org>]

commit bbf9358eba241d6f985c8ecc5efad7115f51f8ac
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Aug 21 00:32:23 2013 +0200

    window: Fix a compiler warning

 src/core/window.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/core/window.c b/src/core/window.c
index e56b0d6..036c839 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -6007,7 +6007,7 @@ meta_window_get_outer_rect (const MetaWindow *window,
 
       if (window->has_custom_frame_extents)
         {
-          GtkBorder *extents = &window->custom_frame_extents;
+          const GtkBorder *extents = &window->custom_frame_extents;
           rect->x += extents->left;
           rect->y += extents->top;
           rect->width -= extents->left + extents->right;