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

[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: e0d3bafd0258 ("V4L/DVB (10954): Add cx231xx USB driver")
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>
(cherry picked from commit 6c3b047fa2d2286d5e438bcb470c7b1a49f415f6)

Orabug: 27208030
CVE: CVE-2017-16536

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>