Session: Fix saving session data on shutdown from project mode

This was broken in d52ee686d1.

Task-number: QTCREATORBUG-13098
Change-Id: Ia075e13fdd00e561b78058a3cab0cb02d2eb5fe6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/modemanager.cpp

@@ -320,7 +320,7 @@ bool ModeManager::isModeSelectorVisible()
     return d->m_modeSelectorVisible;
 }
 
-QObject *ModeManager::instance()
+ModeManager *ModeManager::instance()
 {
     return m_instance;
 }