Fix a bug in the CPU % limiting code

If you attempt to set a pcpu limit that is higher than
110% using rctl (for instance, you want a jail to be
able to use 2 cores on your system so you set pcpu to
200%) the thing you are trying to limit becomes unthrottled.

PR: 189870
Submitted by: dustinwenz@ebureau.com
Reviewed by: trasz
MFC after: 1 week