[gnome-flashback] desktop-background: avoid deprecation warnings

[Alberts Muktupāvels <muktupavels src gnome org>]

commit adeb5768f56a391c48435a8f3bc3b915c48b105c
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Wed Oct 26 01:03:21 2016 +0300

    desktop-background: avoid deprecation warnings

 .../libdesktop-background/gf-desktop-background.c  |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gnome-flashback/libdesktop-background/gf-desktop-background.c 
b/gnome-flashback/libdesktop-background/gf-desktop-background.c
index dae5983..98085ce 100644
--- a/gnome-flashback/libdesktop-background/gf-desktop-background.c
+++ b/gnome-flashback/libdesktop-background/gf-desktop-background.c
@@ -56,8 +56,8 @@ draw_background (GfDesktopBackground *background,
 
   screen = gdk_screen_get_default ();
   root = gdk_screen_get_root_window (screen);
-  width = gdk_screen_get_width (screen);
-  height = gdk_screen_get_height (screen);
+  width = gdk_window_get_width (root);
+  height = gdk_window_get_height (root);
 
   surface = gnome_bg_create_surface (background->bg, root, width, height, TRUE);