thermal: core: Move cdev cleanup to thermal_release()

thermal_release() already frees cdev, let it do rest of the cleanup as
well in order to simplify the error paths in
__thermal_cooling_device_register().

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