tty: let tty_unregister_driver return void

Now that noone checks the return value, switch the return type of
tty_unregister_driver to void. We can do that as we always return zero.

Generally, drivers are not allowed to call tty_unregister_driver while
there are open devices.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-35-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -3525,21 +3525,14 @@ EXPORT_SYMBOL(tty_register_driver);
 /*
  * Called by a tty driver to unregister itself.
  */
-int tty_unregister_driver(struct tty_driver *driver)
+void tty_unregister_driver(struct tty_driver *driver)
 {
-#if 0
-	/* FIXME */
-	if (driver->refcount)
-		return -EBUSY;
-#endif
 	unregister_chrdev_region(MKDEV(driver->major, driver->minor_start),
 				driver->num);
 	mutex_lock(&tty_mutex);
 	list_del(&driver->tty_drivers);
 	mutex_unlock(&tty_mutex);
-	return 0;
 }
-
 EXPORT_SYMBOL(tty_unregister_driver);
 
 dev_t tty_devnum(struct tty_struct *tty)

include/linux/tty.h

@@ -482,7 +482,7 @@ extern void stop_tty(struct tty_struct *tty);
 extern void __start_tty(struct tty_struct *tty);
 extern void start_tty(struct tty_struct *tty);
 extern int tty_register_driver(struct tty_driver *driver);
-extern int tty_unregister_driver(struct tty_driver *driver);
+extern void tty_unregister_driver(struct tty_driver *driver);
 extern struct device *tty_register_device(struct tty_driver *driver,
 					  unsigned index, struct device *dev);
 extern struct device *tty_register_device_attr(struct tty_driver *driver,