sound: Call PCM_RELEASE() if pcm_addchan() fails

Fixes: fd906e47b18f ("sound: Simplify locking during device creation")
Sponsored by: The FreeBSD Foundation
MFC after: 1 day
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D50337

(cherry picked from commit dbfe79bbe5d5ebe296fbff2d101e0994d7881d0d)