acpi_pcib: Trust decoded bus range from _CRS over _BBN

Currently if _BBN doesn't match the first bus in the decoded bus range
from _CRS for a Host to PCI bridge, the driver fails to attach as a
defensive measure.

There is now firmware in the field where these do not match, and the
_BBN values are clearly wrong, so rather than failing attach, trust
the range from _CRS over _BBN.

Co-authored-by: Justin Gibbs <gibbs@FreeBSD.org>
Reported by: gibbs
Reviewed by: imp (earlier version)
Differential Revision: https://reviews.freebsd.org/D42231

(cherry picked from commit 22a6678b627b39ceb94f7323be1010e928d92494)