expat: add fix for CVE-2016-0718

expat: add fix for CVE-2016-0718

Fixes:
CVE-2016-0718 - The Expat XML parser mishandles certain kinds of
malformed input documents, resulting in buffer overflows during
processing and error reporting. The overflows can manifest as a
segmentation fault or as memory corruption during a parse operation. The
bugs allow for a denial of service attack in many applications by an
unauthenticated attacker, and could conceivably result in remote code
execution.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>