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

(cherry picked from commit d7f9a421dfb250e016e3d29b17e2b6a6ae3bc40c)