StDrawingArea: fix texture drawing

cogl_rectangle() wants the four rectangle corners, not the size.

https://bugzilla.gnome.org/show_bug.cgi?id=641745

src/st/st-drawing-area.c

@@ -152,7 +152,7 @@ st_drawing_area_paint (ClutterActor *self)
 
       cogl_set_source (priv->material);
       cogl_rectangle_with_texture_coords (content_box.x1, content_box.y1,
-                                          width, height,
+                                          content_box.x2, content_box.y2,
                                           0.0f, 0.0f, 1.0f, 1.0f);
     }
 }