arm64: dts: rockchip: Lower sd speed on quartz64-b

arm64: dts: rockchip: Lower sd speed on quartz64-b

The previously stated speed of sdr-104 is too high for the hardware
to reliably communicate with some fast SD cards.

Lower this to sd-uhs-sdr50 to fix this.

Fixes: 850960f21f40 ("arm64: dts: rockchip: add Pine64 Quartz64-B device tree")
Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Tested-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20220721044307.48641-1-frattaroli.nicolas@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>