thermal: cpu_cooling: 'freq' can't be zero in cpufreq_state2power()

The frequency table shouldn't have any zero frequency entries and so
such a check isn't required. Though it would be better to make sure
'state' is within limits.

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>