hwmon: convert ntc_thermistor to use devm_thermal_zone_of_sensor_register

hwmon: convert ntc_thermistor to use devm_thermal_zone_of_sensor_register

This changes the driver to use the devm_ version
of thermal_zone_of_sensor_register and cleans
up the  local points and unregister calls.

Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: lm-sensors@lm-sensors.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>