MFC r311953 (by cem)

pciconf(8): Reallow trailing colon in selectors

Reallow device selectors to have a trailing colon, as documented in the
manual page. This was broken along with some unrelated cleanups in
r295806.

PR: 215979
Reported by: David Boyd <David.Boyd49 at twc.com>
Sponsored by: Dell EMC Isilon