TTY: Use the tty_devclass for all usb-serial devices.

drivers/usb/serial/bus.c

@@ -128,6 +128,7 @@ int usb_serial_bus_register(struct usb_serial_device_type *device)
 	device->driver.bus = &usb_serial_bus_type;
 	device->driver.probe = usb_serial_device_probe;
 	device->driver.remove = usb_serial_device_remove;
+	device->driver.devclass = &tty_devclass;
 
 	retval = driver_register(&device->driver);