hwmon: (lm85) Simplify RANGE_TO_REG

Function RANGE_TO_REG can easily be simplified. Credits go to Herbert
Poetzl for indirectly suggesting this to me. I tested that the new
implementation returns the same result as the original implementation
for all input values.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Herbert Poetzl <herbert@13thfloor.at>