gpio: axp209: switch unsigned variables to unsigned int

Checkpatch complains with the following message:
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

Let's make it happy by switching over to unsigned int.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>