arm64: dts: rockchip: rk3399-firefly: remove num-slots from &sdio0 node

The option "num-slots" was deprecated long time ago, so remove it.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20191231191154.5587-1-jbx6244@gmail.com


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