ARM: dts: rockchip: remove cap-mmc-highspeed from rk3188-bqedison2qc mmc1 node

The mmc1 pins are used for SDIO with a wifi chip.
The function mmc_sdio_switch_hs() only checks for MMC_CAP_SD_HIGHSPEED and
not for MMC_CAP_MMC_HIGHSPEED, so cap-mmc-highspeed can be removed.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>