thermal: cpu_cooling: Remove unused cur_freq variable

The 'cur_freq' local variable became unused after commit 84fe2cab
("cpu_cooling: Drop static-power related stuff"), let's remove it.

Cc: Amit Daniel Kachhap <amit.kachhap@gmail.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Javi Merino <javi.merino@kernel.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>