ARM: dts: imx53-ard: Correct Ethernet node name

make dtbs_check:

    lan9220@f4000000: $nodename:0: 'lan9220@f4000000' does not match '^ethernet(@.*)?$'

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>