[cheese] Eliminate an instance-used-via-static warning

[David King <davidk src gnome org>]

commit 02f8e89436ec93d75dafbe06765eef512cb904d3
Author: Nick Black <nick black sprezzatech com>
Date:   Sun Jan 6 17:09:04 2013 +0000

    Eliminate an instance-used-via-static warning

 src/cheese-window.vala |    5 +----
 1 files changed, 1 insertions(+), 4 deletions(-)
---
diff --git a/src/cheese-window.vala b/src/cheese-window.vala
index 3102a1b..30df86d 100644
--- a/src/cheese-window.vala
+++ b/src/cheese-window.vala
@@ -1442,10 +1442,7 @@ public class Cheese.MainWindow : Gtk.ApplicationWindow
       stdout.printf ("Error: %s\n", e.message);
     }
 
-    Gtk.StyleContext context;
-    context = thumb_view.get_style_context ();
-    screen = Gdk.Screen.get_default();
-    context.add_provider_for_screen (screen, css, STYLE_PROVIDER_PRIORITY_USER);
+    Gtk.StyleContext.add_provider_for_screen (screen, css, STYLE_PROVIDER_PRIORITY_USER);
 
     thumb_view.button_press_event.connect (on_thumbnail_mouse_button_press);