ASoC: ac97: use gpiochip data pointer

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: Liam Girdwood <lgirdwood@gmail.com>
Cc: alsa-devel@alsa-project.org
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>