factory: Fix a bug in hardware probing.

A small fix to make sure all the i2c bus are scanned.

BUG=None
TEST=Manually test it on Alex.

Change-Id: I4701cadc6ff1996e8e9b7b1668223907d1752ec5
Reviewed-on: https://gerrit.chromium.org/gerrit/22445
Commit-Ready: Chun-Ta Lin <itspeter@chromium.org>
Reviewed-by: Chun-Ta Lin <itspeter@chromium.org>
Tested-by: Chun-Ta Lin <itspeter@chromium.org>