hwmon: (corsair-psu) Fix fan rpm calculation

The correct fan rpm value is also a LINEAR11 value but without a factor.
Verified by using the fan test button on the psu to let the fan spin up
to maximum for some seconds.

Fixes: 933222c98445 ("hwmon: (corsair-psu) fix unintentional sign extension issue")
Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>
Link: https://lore.kernel.org/r/20201113121954.GA8488@monster.powergraphx.local


Signed-off-by: Guenter Roeck <linux@roeck-us.net>