cpufreq: s5pv210: Use dev_err instead of pr_err in probe

dev_err() allows easily to identify the device printing the message so
no need for __func__.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
[ Viresh: Don't remove update to result variable ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>