Fix DBus signals in Mprisremote

Summary: This seems to fix the issue I mentioned on Telegram/Mail

Test Plan:
Before: Use Mprisremote plugin with App. View did not update when e.g. next is pressed.
Now: View correctly represents the DBus data

Reviewers: #kde_connect

Subscribers: #kde_connect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D12528

plugins/mprisremote/mprisremoteplugin.h

@@ -74,7 +74,7 @@ public:
     Q_SCRIPTABLE void sendAction(const QString& action);
 
 Q_SIGNALS:
-    void propertiesChanged();
+    Q_SCRIPTABLE void propertiesChanged();
 
 private:
     void requestPlayerStatus(const QString& player);