cpufreq: mediatek: Use device print to show logs

- Replace pr_* with dev_* to show logs.
- Remove usage of __func__.

Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>