cpufreq: ARM big LITTLE: put DT nodes after using them

DT nodes should be put using of_node_put() to balance their usage counts. This
is not done properly in ARM's big LITTLE driver. Fix it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>