Input: adp5589-keys - use devm_gpiochip_add_data() for gpios

Input: adp5589-keys - use devm_gpiochip_add_data() for gpios

This change makes use of the devm_gpiochip_add_data() function. With this
the gpiochip_remove() function can be removed, and the
adp5589_gpio_remove() function as well.

The kpad->export_gpio variable is also redundant now, and has been removed.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20201112074308.71351-5-alexandru.ardelean@analog.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>