ARM: simpad: switch to gpiochip_add_data()

We're planning to remove the gpiochip_add() function to swith
to gpiochip_add_data() with NULL for data argument.

Cc: arm@kernel.org
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>