thermal: broadcom: constify thermal_zone_of_device_ops structure

The thermal_zone_of_device_ops structure can be const as it is only
passed as the last argument of thermal_zone_of_sensor_register
and the corresponding parameter is declared as const.

Done with the help of Coccinelle.

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>