Device probe value of BUS_PROBE_NOWILDCARD should be treated specially only
if the device has a fixed devclass. Otherwise it should be interpreted just
as if the driver doesn't want to claim the device.
Prior to this change a device that was not claimed explicitly by its driver
would remain "attached" to the driver that returned BUS_PROBE_NOWILDCARD.
This would bump up the reference on 'driver->refs' and its 'dev->ops' would
point to the 'driver->ops'. When the driver is subsequently unloaded the
'dev->ops->cls' is left pointing to freed memory.
This fixes an easily reproducible #GP fault caused by loading and unloading
vmm.ko multiple times.