apply standard behavior

According to documentation hoverLeaveEvent calls update(), which happens
in QGraphicsItem. As QGraphicsWidget has not been calling parent
implementation that did not happen and e.g. animatedtiles example did
not work correctly.

Change-Id: Ia25dda967bd21298c763996589c63dc173ba6b6a
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>

src/widgets/graphicsview/qgraphicswidget.cpp

@@ -1673,7 +1673,7 @@ void QGraphicsWidget::hoverMoveEvent(QGraphicsSceneHoverEvent *event)
 */
 void QGraphicsWidget::hoverLeaveEvent(QGraphicsSceneHoverEvent *event)
 {
-    Q_UNUSED(event);
+    QGraphicsObject::hoverLeaveEvent(event);
 }
 
 /*!