Input: adp5589 - initialize GPIO controller parent device

While not strictly required for normal operation setting the GPIO parent
device allows the GPIO framework to generate more verbose debug output for
the GPIO chip.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>