cpufreq: dt: eliminate uses of of_node_put()

cpufreq: dt: eliminate uses of of_node_put()

Make use of the __free() cleanup handler to automatically free nodes
when they get out of scope.

Only find_supply_name() is affected, and the new mechanism removes the
need for a 'goto' and the 'name' local variable.

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