audio/oss: Fix build on 14-CURRENT

As of dfff37765ce4ea4fd7db4d293b459dc84008f411 (1400010),
struct device on 14-CURRENT was renamed to struct _device. This
commit chases this change by adding a __FreeBSD_version CPP
conditional.

PR: 259275
Submitted by: cy
Reported by: cy
Reviewed by: crees
Tested by: cy
Approved by: crees
MFH: 2021Q4
Differential Revision: https://reviews.freebsd.org/D32560