Roll FFmpeg DEPS for bug fix.

The test file is a bit too big (30mb) to stick into the regression
tests, so we'll just count on ClusterFuzz for watching this one in
the future.

Pulls in:
96481cb avformat/matroskadec: fix off by 1 error in matroska_read_seek()

BUG=378782
TEST=file no longer crashes.
TBR=wolenetz

Review URL: https://codereview.chromium.org/301223011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274008 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -211,7 +211,7 @@ deps = {
 
   "src/third_party/ffmpeg":
     Var("chromium_git") +
-    "/chromium/third_party/ffmpeg.git@90d4238be2656ee9d6b8f0cdfa5f96d40e6ed7ad",
+    "/chromium/third_party/ffmpeg.git@96481cb9163681998d1407b0c951a4c951be1b04",
 
   "src/third_party/libjingle/source/talk":
     (Var("googlecode_url") % "webrtc") + "/trunk/talk@" +