USB: moved put_bus to its proper place (as the last thing we do shutting down.)

drivers/usb/core/usb.c

@@ -1641,10 +1641,10 @@ static int __init usb_init(void)
  */
 static void __exit usb_exit(void)
 {
-	put_bus(&usb_bus_type);
 	usb_major_cleanup();
 	usbfs_cleanup();
 	usb_hub_cleanup();
+	put_bus(&usb_bus_type);
 }
 
 subsys_initcall(usb_init);