MLK-21863 mx6sabreauto: Fix SD index issue

The imx6qdl-sabreauto-u-boot.dtsi re-alias the usdhc3 to mmc0, and
cause boot issue on mx6sabreauto boards. Remove the re-alias, so
usdhc3 will map to mmc2.

Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/arch/arm/dts/imx6qdl-sabreauto-u-boot.dtsi b/arch/arm/dts/imx6qdl-sabreauto-u-boot.dtsi
index ea90f40..7c078e1 100644
--- a/arch/arm/dts/imx6qdl-sabreauto-u-boot.dtsi
+++ b/arch/arm/dts/imx6qdl-sabreauto-u-boot.dtsi
@@ -5,12 +5,6 @@
 
 #include "imx6qdl-u-boot.dtsi"
 
-/ {
-	aliases {
-		mmc0 = &usdhc3;
-	};
-};
-
 &usdhc3 {
 	no-1-8-v;
 	u-boot,dm-spl;