ProgressManager: Return ProgressManager* from instance

Works better with Qt5-style connects.

Change-Id: I7916369762fa51f24664149f85208b1eb5c7a62e
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/coreplugin/progressmanager/progressmanager.cpp

@@ -737,7 +737,7 @@ ProgressManager::~ProgressManager()
 {
 }
 
-QObject *ProgressManager::instance()
+ProgressManager *ProgressManager::instance()
 {
     return m_instance;
 }