QNX: Fix compiler warning about unused variable.

Change-Id: I16e4aa32647793bf36fee60ed94db69a6ae2d8ea
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qfilesystemwatcher.cpp

@@ -77,6 +77,7 @@ QFileSystemWatcherEngine *QFileSystemWatcherPrivate::createNativeEngine(QObject
 #elif defined(Q_OS_FREEBSD) || defined(Q_OS_MAC)
     return QKqueueFileSystemWatcherEngine::create(parent);
 #else
+    Q_UNUSED(parent);
     return 0;
 #endif
 }