Properly clear a device's devclass if DEVICE_ATTACH() fails if the device does not have a fixed devclass.
Properly clear a device's devclass if DEVICE_ATTACH() fails if the device
does not have a fixed devclass.

Reviewed by:	imp
MFC after:	2 weeks

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