This makes the driver use the data pointer added to the gpio_chip
to store a pointer to the state container instead of relying on
container_of().

Cc: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Cc: Mark Brown <broonie@kernel.org>
Reviewed-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>