cpufreq: mediatek: fix error return code in mtk_cpu_dvfs_info_init()

If regulator_get_voltage() fails, it should return the error code in
mtk_cpu_dvfs_info_init().

Fixes: 0daa4732 ("cpufreq: mediatek: Link CCI device to CPU")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>