dt-bindings: net: dwmac-sun8i: Remove unused address-cells/size-cells

address-cells/size-cells is unnecessary for dwmac-sun8i node.
It was in early days, but since a mdio node is used, it could be
removed.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>