Emit NOTIFY signal for bufferLocked property

Change-Id: Ibc11a06a15834f3486440c65edd397bfcba5e0f4
Reviewed-by: Johan Helsing <johan.helsing@qt.io>
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@hawaiios.org>

src/compositor/compositor_api/qwaylandview.cpp

@@ -307,7 +307,10 @@ bool QWaylandView::isBufferLocked() const
 void QWaylandView::setBufferLock(bool locked)
 {
     Q_D(QWaylandView);
+    if (d->bufferLock == locked)
+        return;
     d->bufferLock = locked;
+    emit bufferLockChanged();
 }
 
 /*!