pinctrl: sunxi: Use common functions to change irq_chip and handler

The current code uses some custom variable affectations, while we have
common functions to do exactly that. Move to the common functions.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>