cpufreq: mediatek: Use scope-based cleanup helper

Replace the manual cpufreq_cpu_put() with __free(put_cpufreq_policy)
annotation for policy references. This reduces the risk of reference
counting mistakes and aligns the code with the latest kernel style.

No functional change intended.

Signed-off-by: Zihuan Zhang <zhangzihuan@kylinos.cn>
[ Viresh: Minor changes ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>