[gtk] css: Fix compiler warning

[Benjamin Otte <otte src gnome org>]

commit 4bb8352ab5c17393032f2a9e7e3ec5ea5a695373
Author: Benjamin Otte <otte redhat com>
Date:   Fri Mar 16 06:04:02 2018 +0100

    css: Fix compiler warning
    
    ...

 gtk/gtkcssimagescaled.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkcssimagescaled.c b/gtk/gtkcssimagescaled.c
index 09166e884c..14108845f1 100644
--- a/gtk/gtkcssimagescaled.c
+++ b/gtk/gtkcssimagescaled.c
@@ -140,7 +140,7 @@ gtk_css_image_scaled_compute (GtkCssImage      *image,
                                            parent_style);
   res->scales[0] = scaled->scales[best];
 
-  return res;
+  return GTK_CSS_IMAGE (res);
 }