DVDInterface: Simplify calling ChangeDisc from CPU thread

When Movie was calling ChangeDisc, it was moving execution to
the host thread just to then make the host thread the CPU thread.
We can simply run the code directly on the CPU thread instead.

Source/Core/DolphinWX/Frame.cpp

@@ -124,7 +124,7 @@ void CRenderFrame::OnDropFiles(wxDropFilesEvent& event)
   }
   else
   {
-    DVDInterface::ChangeDisc(filepath);
+    DVDInterface::ChangeDiscAsHost(filepath);
   }
 }