[gtk+/gtk-style-context] Fix compile warning

[Carlos Garnacho <carlosg src gnome org>]

commit adac15b5c118c9d6231923a6de3028bbd9d067d4
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Nov 3 21:10:06 2010 +0100

    Fix compile warning

 gtk/gtksettings.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtksettings.c b/gtk/gtksettings.c
index 12107a1..29cbd98 100644
--- a/gtk/gtksettings.c
+++ b/gtk/gtksettings.c
@@ -2597,10 +2597,12 @@ settings_update_theme (GtkSettings *settings)
   if (new_provider != provider)
     {
       if (provider)
-        gtk_style_context_remove_provider_for_screen (settings->screen, provider);
+        gtk_style_context_remove_provider_for_screen (settings->screen,
+                                                      GTK_STYLE_PROVIDER (provider));
 
       if (new_provider)
-        gtk_style_context_add_provider_for_screen (settings->screen, new_provider,
+        gtk_style_context_add_provider_for_screen (settings->screen,
+                                                   GTK_STYLE_PROVIDER (new_provider),
                                                    GTK_STYLE_PROVIDER_PRIORITY_SETTINGS + 1);
 
       g_object_set_qdata_full (G_OBJECT (settings), quark_theme_name,