gpio: mm-lantiq: Do not use gpiochip_get_data() in ltq_mm_save_regs()

Commit 6aa7dbfa ("gpio: mm-lantiq: 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: 6aa7dbfa ("gpio: mm-lantiq: use gpiochip data pointer")
Cc: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Cc: John Crispin <blogic@openwrt.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>