arm64: dts: rockchip: Enable UHS-I SDR-50 for Lunzn FastRhino R66S

This board can work in UHS-I SDR-104 mode, but may not be stable,
use SDR-50 instead. Remove the max-frequency property, which is
already defined in rk356x.dtsi.

Fixes: c79dab40 ("arm64: dts: rockchip: Add Lunzn Fastrhino R66S")
Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Link: https://lore.kernel.org/r/20240710143017.685905-4-amadeus@jmu.edu.cn


Signed-off-by: Heiko Stuebner <heiko@sntech.de>