amdtemp: Fix missing 49 degree offset on current EPYC CPUs

On an EPYC 7313P, the temperature reported by amdtemp was off, because
the offset was not applied. Turns out it needs to be applied with one
more condition: https://lkml.org/lkml/2023/4/13/1095

Reviewed by: mhorne
Tested by: mike.jakubik@gmail.com
MFC after: 1 week
Sponsored by: https://www.patreon.com/valpackett
Pull Request: https://github.com/freebsd/freebsd-src/pull/754

(cherry picked from commit c1cbabe8ae5702a1e54d62401fe3b58a84fcb3e4)