Avoid warning on empty expressions

For some reason, Q_UNUSED includes already a semicolon, adding one
on the user side creates an additional empty statement.

Change-Id: I9c5e8fac381345a60792cb75e2938fd53958d3b0
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/qbsprojectmanager/qbscleanstep.cpp

@@ -138,7 +138,7 @@ void QbsCleanStep::cleaningDone(bool success)
 
 void QbsCleanStep::handleTaskStarted(const QString &desciption, int max)
 {
-    Q_UNUSED(desciption);
+    Q_UNUSED(desciption)
     m_maxProgress = max;
 }