[media] cx231xx-cards: fix NULL-deref on missing association descriptor

Make sure to check that we actually have an Interface Association
Descriptor before dereferencing it during probe to avoid dereferencing a
NULL-pointer.

Fixes: e0d3bafd ("V4L/DVB (10954): Add cx231xx USB driver").

Change-Id: Ib3d82edf28ad0a945046cf39cb7d599a5bb6d922
Cc: stable <stable@vger.kernel.org>     # 2.6.30
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Git-commit: 6c3b047fa2d2286d5e438bcb470c7b1a49f415f6
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Krishnamurthy K R <kkr@codeaurora.org>