Fix unused parameter warning

Task-number: QTBUG-68804
Change-Id: Id40ea045237e5ceafc04d86629f2264eecc084c1
Reviewed-by: Liang Qi <liang.qi@qt.io>

src/platformsupport/services/genericunix/qgenericunixservices.cpp

@@ -205,6 +205,8 @@ static inline bool flatpakOpenFile(const QUrl &url)
         QDBusPendingReply<QDBusObjectPath> reply = QDBusConnection::sessionBus().call(message);
         return !reply.isError();
     }
+#else
+    Q_UNUSED(url)
 #endif
 
     return false;