bhyve: Use NVMEV to read the ASQS field of AQA

This is not a functional change, but just being consistent instead of
omitting a shift by 0.

Reviewed by: corvink, chuck, imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D43600

(cherry picked from commit c42692360611c8afce6ee7bb937a858d64a133f4)