arm64: dts: rockchip: set sdmmc0 speed to sd-uhs-sdr50 on rock-3a

As other rk336x based devices, the Rock 3 Model A has issues with high
speed SD cards, so lower the speed to 50 instead of 104 in the same
manor has the Quartz64 Model B has.

Fixes: 22a442e6 ("arm64: dts: rockchip: add basic dts for the radxa rock3 model a")
Signed-off-by: Dan Johansen <strit@manjaro.org>
Link: https://lore.kernel.org/r/20230128112432.132302-1-strit@manjaro.orgSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3568-rock-3a.dts

@@ -732,7 +732,7 @@ &sdmmc0 {
 	disable-wp;
 	pinctrl-names = "default";
 	pinctrl-0 = <&sdmmc0_bus4 &sdmmc0_clk &sdmmc0_cmd &sdmmc0_det>;
-	sd-uhs-sdr104;
+	sd-uhs-sdr50;
 	vmmc-supply = <&vcc3v3_sd>;
 	vqmmc-supply = <&vccio_sd>;
 	status = "okay";