ARM: dts: sunxi: Remove pinctrl size-cells property

The children nodes of the pinctrl node hadn't have any reg property for
quite some time, so we don't need the size-cells property. Remove it.

Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>