arm64: dts: rockchip: fix RockPro64 sdmmc settings

According to the RockPro64 schematic [1] the rk3399 sdmmc controller is
connected to a microSD (TF card) slot. Remove the cap-mmc-highspeed
property of the sdmmc controller, since no mmc card can be connected here.

[1] http://files.pine64.org/doc/rockpro64/rockpro64_v21-SCH.pdf

Fixes: e4f3fb49 ("arm64: dts: rockchip: add initial dts support for Rockpro64")
Signed-off-by: Soeren Moch <smoch@web.de>
Link: https://lore.kernel.org/r/20191004203213.4995-1-smoch@web.deSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-rockpro64.dts

@@ -624,7 +624,6 @@ &saradc {
 
 &sdmmc {
 	bus-width = <4>;
-	cap-mmc-highspeed;
 	cap-sd-highspeed;
 	cd-gpios = <&gpio0 7 GPIO_ACTIVE_LOW>;
 	disable-wp;