CHERRY-PICK: Stout - Fix EC version reported by mosys.

According to spec, revision 'A' starts at lower nibble = 1, B = 2, etc.
Mosys uses A = 0, B = 1, etc. Fix this, and make value 0 = no revision.

BUG=chrome-os-partner:15698
TEST=mosys ec info, check version number matches expectation.
BRANCH=stout

Change-Id: I7d443ed9fd7415ef5481e38a180445d2d4732505
Original-Change-Id: I51784286c5c27dd9bfabde6663a9cc69c378ba2a
Reviewed-on: https://gerrit.chromium.org/gerrit/36916
Tested-by: Shawn Nematbakhsh <shawnn@google.com>
Reviewed-by: David Hendricks <dhendrix@chromium.org>