Correct a header path for sync.h in libsync

Not all sources lists have been kept up to date with code
movement/removal and it seems to make some isolate steps in
cq sad for some CLs (mine).

Change-Id: I37b2cff42454a5f4c49eb947289c279701639868
Reviewed-on: https://chromium-review.googlesource.com/c/1288972
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#602773}
1 file changed