sound: Remove unnecessary uio checks in dsp_io_ops()

uiomove_faultflag() takes care of that already.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D53733

(cherry picked from commit 6b5431941c10b6fdf164ad9d3dfa4b4f1b2edc22)