Add TSAN suppression for heap-use-after-free in libvpx

BUG=3671
R=kjellander@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/18199004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6937 4adac7df-926f-26a2-2b94-8c16560cd09d