bhyve(8): fix manpage formatting

In commit 67c26eb2a57 a stray ".El" was introduced, breaking
formatting of options.

Reviewed by: corvink, markj
Fixes: 67c26eb2a57c ("bhyve: add cmdline option for TPM emulation")
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D42434