gpio: mpc8xxx: Do not use gpiochip_get_data() in mpc8xxx_gpio_save_regs()

Commit 709d71a1 ("gpio: mpc8xxx: use gpiochip data pointer") replaces
the use of container_of() with gpiochip_get_data(). However, the data
pointer is not yet set by the time the save_regs function is called.

Fixes: 709d71a1 ("gpio: mpc8xxx: use gpiochip data pointer")
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>