Fix following coccichek error:
./drivers/cpufreq/mediatek-cpufreq.c:199:2-8: preceding lock on line
./drivers/cpufreq/mediatek-cpufreq.c:208:2-8: preceding lock on line

mutex_lock is acquired but not released before return.
Use 'goto out' to help releasing the mutex_lock.

Fixes: c210063b ("cpufreq: mediatek: Add opp notification support")
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Reviewed-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>