Fix bug reported by Mike Brown <mbrown@vmware.com>, in which a

Fix bug reported by Mike Brown <mbrown@vmware.com>, in which a
secondary device was always detected on an IDE channel that had a
primary device.  Both qemu and Bochs report error/lbam/lbah register
values that are invalid for a device that exists in such a situation,
but GSX Server reports 1/0/0, which indicates a valid device.
Fortunately, GSX Server does report a useful value in the status
register, so the bug fix adds a check for that value also.