hfs: fix coverity-found null deref

Fix potential null deref introduced by commit
cf059462


http://bugzilla.kernel.org/show_bug.cgi?id=9748

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Reported-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>