thermal: broadcom: use devm_thermal_zone_of_sensor_register

Using devm_thermal_zone_of_sensor_register allows to simplify some
error handling code, drop a label, and drop the remove function.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>