DolphinQt: Fix ControllersPane group box spacing.

Source/Core/DolphinQt/Config/ControllersPane.cpp

@@ -32,4 +32,5 @@ void ControllersPane::CreateMainLayout()
   layout->addWidget(gamecube_controllers);
   layout->addWidget(m_wiimote_controllers);
   layout->addWidget(common);
+  layout->addStretch(1);
 }