LM73: fix temperature sensor on SANTARO/SANTOKA

For SANTARO/SANTOKA the board temperature sensor was declared as
"national,lm75" in the device-tree resulting in the LM73 sensor
equipped on these system being treated as LM75 and therefore giving
wrong temperature read-outs.

This patch declares the temperature correctly as "national,lm73", which
results in proper temperature read-outs.

YT-348