Like other drivers silently unregister_tty_driver and put_tty_driver.  It
shouldn't be busy when module release function is called, since we are not
bsd, no refs shouldn't be held.

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>