hwmon: (lm70) Allow 4wire SPI bus with LM70

Removing the 3wire limitation on LM70 as the component also allows
operation on 4wire SPI bus

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>