hwmon: (gpio-fan) Get rid of platform data struct

We are not passing the platform data struct into the driver from the
outside, there is no point of having it around separately so instead
of first populating the platform data struct and assigning the result
into the same variables in the state container (struct gpio_fan_data)
just assign the configuration from the device tree directly into the
state container members.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>