Widen suppressions for another FFmpeg roll.

TSAN doesn't comprehend the atomic ref count operation.

BUG=239350
TEST=none
TBR=jyasskin
NOTRY=true

Review URL: https://codereview.chromium.org/294663011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272002 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/tsan/suppressions.txt

@@ -917,12 +917,19 @@
   fun:gfx::GtkInitFromCommandLine
 }
 {
-  bug_239350
+  bug_239350_a
   ThreadSanitizer:Race
   fun:av_buffer_unref
   fun:av_frame_unref
   ...
 }
+{
+  bug_239350_b
+  ThreadSanitizer:Race
+  fun:av_buffer_get_opaque
+  fun:av_buffer_get_opaque
+  ...
+}
 {
   bug_256792
   ThreadSanitizer:Race