[PATCH] ieee1394: fix cross_bound check for null ISO packets

Fix cross_bound to not return 1 for zero-length regions.  Fixes regression
when sending null ISO packets.

Signed-off-by: Jody McIntyre <scjody@steamballoon.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>