Fix bhyve's NVMe Completion Queue entry values

Fix bhyve's NVMe Completion Queue entry values

The function which processes Admin commands was not returning the
Command Specific value in Completion Queue Entry, Dword 0 (CDW0). This
effects commands such as Set Features, Number of Queues which returns
the number of queues supported by the device in CDW0. In this case, the
host will only create 1 queue pair (Number of Queues is zero based).
This also masked a bug in the queue counting logic.

Reviewed by: imp, araujo
Approved by: imp (mentor)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D18703