qmlvideo example, add missing #ifdef PERFORMANCEMONITOR_SUPPORT

This usage of PerformanceMonitor needs to be protected by the same
preprocessor check as the header include that makes it available.

Change-Id: Ie8a1b6e99a61c333ceedcf2e9751235fc2efb415
Reviewed-by: Martin Smith <martin.smith@digia.com>

examples/multimedia/video/qmlvideo/main.cpp

@@ -67,7 +67,9 @@ int main(int argc, char *argv[])
     QString source1, source2;
     qreal volume = 0.5;
     QStringList args = app.arguments();
+#ifdef PERFORMANCEMONITOR_SUPPORT
     PerformanceMonitor::State performanceMonitorState;
+#endif
     bool sourceIsUrl = false;
     for (int i = 1; i < args.size(); ++i) {
         const QByteArray arg = args.at(i).toUtf8();