Fix character case in examples for "camcontrol security" - should be
"-U user" not "-u user".

PR:		193179
Submitted by:	milios ccsys com
MFC after:	3 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270872 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f