hwmon: (core) constify thermal_zone_of_device_ops structures

The thermal_zone_of_device_ops structure is only passed as the fourth
argument to devm_thermal_zone_of_sensor_register, which is declared
as const.  Thus the thermal_zone_of_device_ops structure itself can
be const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>