gpio: Fix bit masking in Kontron PLD GPIO driver

This patch fixes the bit masking within the GPIO driver. The masking is
basically done twice which causes the wrong GPIOs to be addressed.

Signed-off-by: Michael Brunner <michael.brunner@kontron.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>