PM / devfreq: tegra30: Use resource-managed helpers

Use resource-managed API helpers to simplify driver's probe() function,
making code cleaner.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>