bhyve: use a fixed 32 bit BAR base address

OVMF always uses 0xC0000000 as base address for 32 bit PCI MMIO space.
For that reason, we should use that address too.

Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D31051
Sponsored by: Beckhoff Automation GmbH & Co. KG

(cherry picked from commit 5cf21e48ccf114928da9c6564c7e5dec7d6119c5)

bhyve: Fix compile

We need err.h

Fixes: 5cf21e48ccf11 ("bhyve: use a fixed 32 bit BAR base address")
Sponsored by: Bechoff Automation GmbH & Co. KG

(cherry picked from commit fc7207c87795da4533dc7f97287638f6da85b3b0)