bhyve nvme: Fix Active Firmware Info

Summary:
Currently Active Firmware Info is not initialized.

Fix is to initialize the Active Firmware Info to Slot 1.

Test Plan: Within FreeBSD/Linux guests, show the Firmware Logpage to confirm.

Reviewed By: chuck
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D32658

(cherry picked from commit 3cae10048d27f805d7fc909b123ddee34be0268e)