gpio: pca953x: 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: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Markus Pargmann <mpa@pengutronix.de>
Cc: Toby Smith <toby@tismith.id.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>