thermal: cpu_cooling: initialize 'cpufreq_val' on registration

There is no point checking for validity of 'cpufreq_val' from
cpufreq_thermal_notifier() every time the routine is called. Its guaranteed to
be 0 on the first call but will be valid otherwise.

Lets update it once while the device registers.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>