sysutils/devcpu-data-amd: Specify the hash to fetch

Fetching the latest revision of these firmware files could result in a
checksum mismatch if the files were updated in the upstream repository.
By downloading a specific revision, we prevent this potential problem.

Reported by: diizzy
Approved by: sbruno (maintainer)
Differential Revision: https://reviews.freebsd.org/D32969