Implement device unbusying via a cdevpriv destructor.
Implement device unbusying via a cdevpriv destructor.

Suggested by:	jhb
Tested by:	Mark Johnston <mjohnston at sandvine dot com>
Reviewed by:	emaste, jhb
MFC after:	10 days
X-MFC:		r212661

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase