Fix warning in qobject.cpp

Variable only used in debug mode

Change-Id: I6601ca68c427b909680423ae81802f1ed5cd178a
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@nokia.com>

src/corelib/kernel/qobject.cpp

@@ -2385,6 +2385,7 @@ QMetaObject::Connection QObject::connect(const QObject *sender, const char *sign
     int signalOffset, methodOffset;
     computeOffsets(smeta, &signalOffset, &methodOffset);
     int signal_absolute_index = signal_index + methodOffset;
+    Q_UNUSED(signal_absolute_index) //only used in debug mode
     signal_index += signalOffset;
 
     QByteArray tmp_method_name;