TTY: tty3270, free tty driver properly

On module unload, in tty3270_exit, we forgot to free the tty driver.
Add there a call to put_tty_driver.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux390@de.ibm.com
Cc: linux-s390@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/s390/char/tty3270.c

@@ -1800,6 +1800,7 @@ tty3270_exit(void)
 	driver = tty3270_driver;
 	tty3270_driver = NULL;
 	tty_unregister_driver(driver);
+	put_tty_driver(driver);
 	tty3270_del_views();
 }