[gtk] Fix compiler warnings

[Matthias Clasen <matthiasc src gnome org>]

commit 81055ca7d97839a03f5a43632da61fdac11ddb8c
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Feb 8 07:55:41 2019 -0500

    Fix compiler warnings
    
    Fallout from recent GtkStackPage changes.

 gtk/gtkstacksidebar.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkstacksidebar.c b/gtk/gtkstacksidebar.c
index 4e42e1ea2d..bf1b13759d 100644
--- a/gtk/gtkstacksidebar.c
+++ b/gtk/gtkstacksidebar.c
@@ -275,7 +275,7 @@ add_child (GtkWidget       *widget,
   GtkStackSidebarPrivate *priv = gtk_stack_sidebar_get_instance_private (sidebar);
   GtkWidget *item;
   GtkWidget *row;
-  GObject *page;
+  GtkStackPage *page;
 
   /* Check we don't actually already know about this widget */
   if (g_hash_table_lookup (priv->rows, widget))
@@ -320,7 +320,7 @@ remove_child (GtkWidget       *widget,
 
   if (priv->stack)
     {
-      GObject *page = gtk_stack_get_page (GTK_STACK (priv->stack), widget);
+      GtkStackPage *page = gtk_stack_get_page (GTK_STACK (priv->stack), widget);
       if (page)
         {
           g_signal_handlers_disconnect_by_func (page, on_child_updated, sidebar);