sound: use device_set_descf() to set device descriptions

Commit 6b6914c1e21b introduced a printf-like version of
device_set_desc(), so use it to simplify device description setting in
the audio stack.

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Reviewed by: dev_submerge.ch, markj
Differential Revision: https://reviews.freebsd.org/D43467