bhyve: avoid uninitialized variable

Reviewed by: markj
Signed-off-by: Corvin Köhne <c.koehne@beckhoff.com>
Reported-by: Andy Fiddaman <andy@omniosce.org>
Differential Revision: https://reviews.freebsd.org/D34688
(cherry picked from commit 8ac8adda8dbaceebd296e4fd7df36b7a8db7f6d3)