hwmon: (lm90) Convert some macros to static functions

Use static functions instead of the TEMPx_FROM_REG* and TEMPx_TO_REG*
macros.  This will ensure type safety and eliminate any side effects
from arguments passed in since the macros referenced 'val' multiple
times.  This change should not affect functionality.

Signed-off-by: Nate Case <ncase@xes-inc.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Martyn Welch <martyn.welch@gefanuc.com>