cpufreq: sun50i: Switch to use dev_err_probe() helper

In the probe path, convert pr_err() to dev_err_probe() which will
check if error code is -EPROBE_DEFER and prints the error name.
It also sets the defer probe reason which can be checked later
through debugfs. It's more simple in error path.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>