bhyve: do not exit if LPC finds no host selector

The host selector is only required when the user likes to use the same
LPC device IDs as the physical LPC device. This is an uncommon use case.
For that reason, it makes no sense to exit when we don't find the host
selector.

Reviewed by: markj
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D39311