arm64: dts: rockchip: Lower SD card speed on rk3399 Pinebook Pro

MicroSD card slot in the Pinebook Pro is located on a separate
daughterboard that's connected to the mainboard using a rather
long flat cable.  The resulting signal degradation causes many
perfectly fine microSD cards not to work in the Pinebook Pro,
which is a common source of frustration among the owners.

Changing the mode and lowering the speed reportedly fixes this
issue and makes many microSD cards work as expected.

Co-developed-by: Dragan Simic <[email protected]>
Signed-off-by: Dragan Simic <[email protected]>
Tested-by: JR Gonzalez <[email protected]>
Signed-off-by: Dan Johansen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Heiko Stuebner <[email protected]>

Author: Strit

arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts

@@ -943,7 +943,7 @@
 	disable-wp;
 	pinctrl-names = "default";
 	pinctrl-0 = <&sdmmc_clk &sdmmc_cmd &sdmmc_bus4>;
-	sd-uhs-sdr104;
+	sd-uhs-sdr50;
 	vmmc-supply = <&vcc3v0_sd>;
 	vqmmc-supply = <&vcc_sdio>;
 	status = "okay";