[PATCH] i4l fix DLE masking in isdn_tty_try_read

DLE masking was non-functional since the new tty handling.

Found by Peter Evertz <leo2@pec.homeip.net>

Signed-off-by: Karsten Keil <kkeil@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>