ddress-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.

This patch fix the following DT warning:
Warning (avoid_unnecessary_addr_size): /soc/ethernet@1c50000: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>