Fix freebsd32 support for PCIOCGETCONF.

This fixes regresssions in pciconf -l and some ports as reported on
freebsd-current:

https://lists.freebsd.org/pipermail/freebsd-current/2018-November/072144.html

Reported by: jbeich
Reviewed by: kib (also proposed an idential patch)
Tested by: jbeich
MFC after: 3 days
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D18011