hwmon: (max31790) Set correct PWM value

Traced fans not spinning to incorrect PWM value being written.
The passed in value was written instead of the calulated value.

Fixes: 54187ff9 ("hwmon: (max31790) Convert to use new hwmon registration API")
Signed-off-by: Alex Hemme <ahemme@cisco.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>