arm64: dts: rockchip: fix RockPro64 sdmmc settings

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: d0b34973932d ("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.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>