thermal: cpu_cooling: get rid of a variable in cpufreq_set_cur_state()

'cpu' is used at only one place and there is no need to keep a separate
variable for it.

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>