cpufreq: dt: call of_node_put() before error out

If of_match_node() fails, this init function bails out without
calling of_node_put().

Also change of_node_put(of_root) to of_node_put(np); both of them
hold the same pointer, but it seems better to call of_node_put()
against the node returned by of_find_node_by_path().

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>