USB: serial: use tty_port_register_device()

We already have the tty port when probing a usb-serial port so use
tty_port_register_device() directly instead of tty_port_install() later
to set up the port link.

This is a step towards enabling serdev for usb-serial (but we need to
determine how to handle hotplugging first).

Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>

drivers/usb/serial/bus.c

···
 	}
 
 	minor = port->minor;
-	tty_dev = tty_register_device(usb_serial_tty_driver, minor, dev);
+	tty_dev = tty_port_register_device(&port->port, usb_serial_tty_driver,
+					   minor, dev);
 	if (IS_ERR(tty_dev)) {
 		retval = PTR_ERR(tty_dev);
 		goto err_port_remove;

drivers/usb/serial/usb-serial.c

···
 	if (retval)
 		goto error_get_interface;
 
-	retval = tty_port_install(&port->port, driver, tty);
+	retval = tty_standard_install(driver, tty);
 	if (retval)
 		goto error_init_termios;