linux-phytec-fsl

gpio: bt8xx: 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: Michael Buesch <m@bues.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>