thermal: cpu_cooling: remove cpufreq_cooling_get_level()

There is only one user of cpufreq_cooling_get_level() and that already
has pointer to the cpufreq_cdev structure. It can directly call
get_level() instead and we can get rid of cpufreq_cooling_get_level().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>