hid: cp2112: 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: linux-input@vger.kernel.org
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>