arm64: dts: meson-g12a: Fix internal Ethernet PHY unit name

Documentation/devicetree/bindings/net/ethernet-phy.yaml defines that the
node name for Ethernet PHYs should match the following pattern:
  ^ethernet-phy(@[a-f0-9]+)?$

Replace the underscore with a hyphen to adhere to this binding.

Fixes: 280c17df ("arm64: dts: meson: g12a: add mdio multiplexer")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230111211350.1461860-6-martin.blumenstingl@googlemail.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>