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: Srinivas Kandagatla <srinivas.kandagatla@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>