[gnome-control-center/wip/jsparber/background: 22/45] background: fix build warning by casting obj to gtkWidget

[Julian Sparber <jsparber src gnome org>]

commit 70e0b730190f9b459c09137d62ae8be54de2a7e3
Author: Julian Sparber <julian sparber net>
Date:   Thu Nov 23 21:27:47 2017 +0100

    background: fix build warning by casting obj to gtkWidget
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788515<Paste>

 panels/background/cc-background-grid-item.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/panels/background/cc-background-grid-item.c b/panels/background/cc-background-grid-item.c
index ccdd138..87eeb8b 100644
--- a/panels/background/cc-background-grid-item.c
+++ b/panels/background/cc-background-grid-item.c
@@ -254,7 +254,7 @@ cc_background_grid_item_init (CcBackgroundGridItem *self)
   g_signal_connect (G_OBJECT (drawing), "draw",
                     G_CALLBACK (on_gallery_item_draw), self);
 
-  gtk_widget_set_size_request (self, 250, 200);
+  gtk_widget_set_size_request (GTK_WIDGET(self), 250, 200);
   gtk_widget_show (drawing);
   gtk_container_add (GTK_CONTAINER (self), drawing);
 }