rockchip: rk3308: add alias for emmc/sdmmc

Add alias for mmc/sdmmc so that we can have a fix mmc number for emmc.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/arm/dts/rk3308-u-boot.dtsi b/arch/arm/dts/rk3308-u-boot.dtsi
index f5a5953..4bfad31 100644
--- a/arch/arm/dts/rk3308-u-boot.dtsi
+++ b/arch/arm/dts/rk3308-u-boot.dtsi
@@ -3,6 +3,13 @@
  *(C) Copyright 2019 Rockchip Electronics Co., Ltd
  */
 
+/ {
+	aliases {
+		mmc0 = &emmc;
+		mmc1 = &sdmmc;
+	};
+};
+
 &cru {
 	u-boot,dm-pre-reloc;
 };