cpufreq: ti-cpufreq: add missing of_node_put()

call of_node_put to release the refcount of np.

Signed-off-by: Zumeng Chen <zumeng.chen@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>