Add missing error handling when registering the tty device at port
probe. This avoids trying to remove an uninitialised character device
when the port device is removed.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: NTakashi Iwai <tiwai@suse.de>
Cc: stable <stable@vger.kernel.org>	# v2.6.12
Signed-off-by: NJohan Hovold <johan@kernel.org>
Acked-by: NGreg Kroah-Hartman <greg@kroah.com>