gpio: Fix platform driver name in Kontron PLD GPIO driver

This patch changes the driver name to be consistent with the name that
is registered as cell name in the MFD driver. Otherwise the driver won't
load.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Kevin Strasser <strassek@engr.orst.edu>
Signed-off-by: Michael Brunner <michael.brunner@kontron.com>