gpio: kempld: Fix autoloading of module

Make the module alias match the platform device name, so gpio-kempld module
should now autoload correctly.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>