add Q_OBJECT to QMediaGaplessPlaybackControl

Change-Id: I010b14f7900bd168012bb876f708397eec4dfa4b
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/multimedia/qmediagaplessplaybackcontrol.h

@@ -52,6 +52,7 @@ QT_MODULE(Multimedia)
 
 class Q_MULTIMEDIA_EXPORT QMediaGaplessPlaybackControl : public QMediaControl
 {
+    Q_OBJECT
 public:
     virtual ~QMediaGaplessPlaybackControl();