[gtk] popover: Fix a broken cast

[Timm Bäder <baedert src gnome org>]

commit 92a79d3f963a4d486452e7efdf26b90f5518d122
Author: Timm Bäder <mail baedert org>
Date:   Sat Jul 13 17:06:22 2019 +0200

    popover: Fix a broken cast
    
    The widget passed here is priv->relative_to, not the popover.

 gtk/gtkpopover.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkpopover.c b/gtk/gtkpopover.c
index 9781c1a13e..87d888bd34 100644
--- a/gtk/gtkpopover.c
+++ b/gtk/gtkpopover.c
@@ -683,7 +683,7 @@ surface_transform_changed_cb (GtkWidget               *widget,
                               const graphene_matrix_t *transform,
                               gpointer                 user_data)
 {
-  GtkPopover *popover = GTK_POPOVER (widget);
+  GtkPopover *popover = user_data;
   GtkPopoverPrivate *priv = gtk_popover_get_instance_private (popover);
 
   move_to_rect (popover);