arm64: dts: meson-axg: use the proper compatible for ethmac

Use the correct compatible for the AXG ethernet mac node.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>