arm64: dts: stratix10: remove 'num-slots' property for dwmmc

Since 'num-slots' had already deprecated, remove the property in
device-tree file.
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

arch/arm64/boot/dts/altera/socfpga_stratix10_socdk.dts

@@ -88,7 +88,6 @@ phy0: ethernet-phy@0 {
 
 &mmc {
 	status = "okay";
-	num-slots = <1>;
 	cap-sd-highspeed;
 	broken-cd;
 	bus-width = <4>;