[PATCH] i4l/isdn_tty.c: fix a check-after-use

Fix a check-after-use spotted by the Coverity checker.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>