mvebu: fix missing property in puzzle thermal

mvebu: fix missing property in puzzle thermal

Fix missing property in puzzle thermal. The thing was never supposed to
work.

Property #thermal-sensor-cells was missing from the puzzle hwmon, making
the entire thermal platform referencing that fail to probe with -EINVAL.

The puzzle hwmon expose 2 termistor but they probably use an userspace
downstream utility to configure and handle thermal. For this reason we
really don't know what they use the sensor for or when it's attached.

We use them to sensor if the Chassis gets too hot due to ambient
temperature and generic components getting too warm.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>