thermal: cpu_cooling: use cpufreq_dev_list instead of cpufreq_dev_count

As we already have a list of cpufreq_cooling_devices now, lets use it instead of
a local counter.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
(cherry picked from commit 2479bb6443d6a793f896219a34bfab0cc410f0b4)
Signed-off-by: Kevin Hilman <khilman@linaro.org>