cpufreq: qcom-nvmem: eliminate uses of of_node_put()

Make use of the __free() macro to automate memory deallocation when
the existing device nodes get out of scope, removing the need for
of_node_put() and therefore increasing code safety if more error paths
are added to the driver, which could miss the required of_node_put()
as it already occurred with commit '57f2f8b4 ("cpufreq: qcom:
Refactor the driver to make it easier to extend")'.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>