CrOS: Update Chromite pin.
CrOS: Update Chromite pin.

Update ChromeOS Chromite pins.
- [master]
  a9f0afd788daa98004dc2674fadc9a350af0ad08 =>
     189b76e96b612f494227b4d0b103f59eefda8e83

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/1702163002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@298812 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build