ARM: dts: bcm283x: fix ethernet node name

It should be "ethernet@x" instead of "usbether@x" as required by Ethernet
controller devicetree schema:
 Documentation/devicetree/bindings/net/ethernet-controller.yaml

This patch can potentially affect boot loaders patching against full
node path instead of using device aliases.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>