TTY: drop driver reference in tty_open fail path

When tty_driver_lookup_tty fails in tty_open, we forget to drop a
reference to the tty driver. This was added by commit 4a2b5fddd5 (Move
tty lookup/reopen to caller).

Fix that by adding tty_driver_kref_put to the fail path.

I will refactor the code later. This is for the ease of backporting to
stable.

Introduced-in: v2.6.28-rc2
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: stable <stable@vger.kernel.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Acked-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
void tty_free_termios(struct tty_struct *tty)
{
	struct ktermios *tp;
	int idx = tty->index;
	/* Kill this flag and push into drivers for locking etc */
	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
		/* FIXME: Locking on ->termios array */
		tp = tty->termios;
		tty->driver->termios[idx] = NULL;
		kfree(tp);
	}
}

void tty_free_termios(struct tty_struct *tty)
{
	struct ktermios *tp;
	int idx = tty->index;
	/* Kill this flag and push into drivers for locking etc */
	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
		/* FIXME: Locking on ->termios array */
		tp = tty->termios;
		tty->driver->termios[idx] = NULL;
		kfree(tp);
	}
}
