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/texteditor/codeassist/codeassistant.cpp

@@ -554,7 +554,7 @@ bool CodeAssistantPrivate::isDestroyEvent(int key, const QString &keyText)
 
 bool CodeAssistantPrivate::eventFilter(QObject *o, QEvent *e)
 {
-    Q_UNUSED(o);
+    Q_UNUSED(o)
 
     if (isWaitingForProposal()) {
         QEvent::Type type = e->type();