ARM: shmobile: bockw: fixup ether node naming

According to the ePAPR spec,
the node name should be "ethernet", not "lan0".

Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>