sbin/veriexec: fixed parameter parsing of option -x

The -x parameter doesn't take any arguments. It says that all further
arguments are paths to check.

Reviewed by: imp@
Sponsored by: Netflix
Pull Request: https://github.com/freebsd/freebsd-src/pull/443/files

(cherry picked from commit e5be21d19b41e4d42ffea5c7978d7e64a5cec4fc)