Additional suppression for TSan deadlock detection

Turns out the one in https://webrtc-codereview.appspot.com/44899004
was not enough to suppress this error.

TBR=pbos@webrtc.org
BUG=4456
TESTED=Passing local TSan run of rtc_unittests

Review URL: https://webrtc-codereview.appspot.com/51479004

Cr-Commit-Position: refs/heads/master@{#8883}
1 file changed