smbus manuals: include term SMBus in description

Fixes: 5ad3b09f2fe9 (smb: distinguishable descriptions)
MFC after: 3 days
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/

(cherry picked from commit 8ccdf86ee57575b04983bc7be68c357fb83668f8)