dt-bindings: net: rockchip-dwmac: use rgmii-id in example

dt-bindings: net: rockchip-dwmac: use rgmii-id in example

The dwmac supports specifying the RGMII clock delays, but it is
recommended to use rgmii-id and to specify the delays in the phy node
instead [1].

Change the example accordingly to no longer promote this undesired
setting.

[1] https://lore.kernel.org/all/1a0de7b4-f0f7-4080-ae48-f5ffa9e76be3@lunn.ch/

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240408-rockchip-dwmac-rgmii-id-binding-v1-1-3886d1a8bd54@pengutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>