sound: Rename chn_* feeder functions to feeder_*
Avoid layering violation. No functional change intended.
Sponsored by: The FreeBSD Foundation
MFC after: 2 days
Reviewed by: dev_submerge.ch
Differential Revision: https://reviews.freebsd.org/D45983
(cherry picked from commit 29ff7b08be363f0d4345794bb951d5c0c8406a0a)