cpufreq / ondemand: update frequency when limits are relaxed

Reevaluate CPU load and update frequency immediately whenever limits
are changed. Currently ondemand doesn't do that when limits are
relaxed, wasting power on systems with relatively low sampling rate.

Signed-off-by: Michal Pecio <mpecio@nvidia.com>
Reviewed-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>