USB: serial: bus: fix const issue in usb_serial_device_match()

usb_serial_device_match() takes a const pointer, and then decides to
cast it away into a non-const one, which is not a good thing to do
overall. Fix this up by properly setting the pointers to be const to
preserve that attribute.

Fixes: d69d80484598 ("driver core: have match() callback in struct bus_type take a const *")
Signed-off-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>

drivers/usb/serial/bus.c

···
 				   const struct device_driver *drv)
 {
 	const struct usb_serial_port *port = to_usb_serial_port(dev);
-	struct usb_serial_driver *driver = to_usb_serial_driver(drv);
+	const struct usb_serial_driver *driver = to_usb_serial_driver(drv);
 
 	/*
 	 * drivers are already assigned to ports in serial_probe so it's