attestation: Fix include directories

Assume (for now) that `src/platform2` will be copied by emerge into a temp
`platform2-9999` directory. So we'll have a structure like this::

    platform2-9999
        chaps
        common-mk
        ...
        platform2
            attestation
            buffet
            ...

When current repositories in `src/platform` are migrated to `src/platform2`,
we need to fix this again.

BUG=chromium:345099
TEST=See CL:188254
Change-Id: Iac212b1803b04ba3a40971d4530d4ba99cae6f3d
1 file changed
tree: a8872a047cbc9be498f93f2ccb3b724fac39ee16
  1. attestation/
  2. LICENSE