Fix dead link

[Arnie97]

Make sure all boxes are checked (add x inside the brackets) when you submit your contribution, remove this sentence before doing so.

• This PR is for the dev branch rather than for the release branch.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at docs/*.

To be completed below: Description of and rationale behind this PR:

The header files were moved into include in the commit https://review.coreboot.org/plugins/gitiles/flashrom/+/87d7b110d6ed6d4ef0b61e777f2fee3c10808f0b

[marcelstoer]

Thanks