mips: lantiq: xway: sysctrl: rename the etop node

Bindig requires a node name matching ‘^ethernet@[0-9a-f]+$’. This patch
changes the clock name from “etop” to “ethernet”.

This fixes the following warning:
arch/mips/boot/dts/lantiq/danube_easy50712.dtb: etop@e180000 (lantiq,etop-xway): $nodename:0: 'etop@e180000' does not match '^ethernet@[0-9a-f]+$'
	from schema $id: http://devicetree.org/schemas/net/lantiq,etop-xway.yaml#



Fixes: dac0bad9 ("dt-bindings: net: lantiq,etop-xway: Document Lantiq Xway ETOP bindings")
Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Acked-by: Jakub Kicinski <kuba@kernel.org>