[PATCH] epca: prevent panic on tty_register_driver() failure

Make epca fail on initialization failure instead of panic.

Cc: "Digi International, Inc" <Eng.Linux@digi.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Acked-by: Scott Kilau <scottk@digi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>