usb: gadget: langwell: convert to new style

with this patch we can finally remove the global
"the_controller" pointer.

Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/langwell_udc.h b/drivers/usb/gadget/langwell_udc.h
index 1bec66f..ef79e24 100644
--- a/drivers/usb/gadget/langwell_udc.h
+++ b/drivers/usb/gadget/langwell_udc.h
@@ -221,3 +221,5 @@
 	u16			dev_status;
 };
 
+#define gadget_to_langwell(g)	container_of((g), struct langwell_udc, gadget)
+