thermal/of: Fix reference leak in thermal_of_cm_lookup()

In the Linux kernel, the following vulnerability has been resolved:

thermal/of: Fix reference leak in thermal_of_cm_lookup()

In thermal_of_cm_lookup(), tr_np is obtained via of_parse_phandle(), but

never released.

Use the __free(device_node) cleanup attribute to automatically release

the node and fix the leak.

[ rjw: Changelog edits ]