ARM: dts: rockchip: fix phy nodename for rk3229-xms6

A test with the command below gives for example this error:

arch/arm/boot/dts/rk3229-xms6.dt.yaml: phy@0:
'#phy-cells' is a required property

The phy nodename is normally used by a phy-handle.
This node is however compatible with
"ethernet-phy-id1234.d400", "ethernet-phy-ieee802.3-c22"
which is just been added to 'ethernet-phy.yaml'.
So change nodename to 'ethernet-phy' for which '#phy-cells'
is not a required property

make ARCH=arm dtbs_check
DT_SCHEMA_FILES=~/.local/lib/python3.5/site-packages/dtschema/schemas/
phy/phy-provider.yaml

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20200416170321.4216-2-jbx6244@gmail.com