wayland: Fix PrepareForSleep dbus connection

This is a typo. We must use the path of the manager rather than the
session path, which is not initialized yet.

src/logind.cpp

@@ -222,7 +222,7 @@ void LogindIntegration::logindServiceRegistered()
     );
 
     m_bus.connect(m_sessionControllerService,
-                  m_sessionPath,
+                  m_sessionControllerPath,
                   m_sessionControllerManagerInterface,
                   QStringLiteral("PrepareForSleep"),
                   this,