ARM: dts: ast2500: Update SDHCI nodes

Match the description used by the Linux kernel, except use scu instead
of syscon as the phandle.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/arch/arm/dts/ast2500-evb.dts b/arch/arm/dts/ast2500-evb.dts
index 874e042..cc57776 100644
--- a/arch/arm/dts/ast2500-evb.dts
+++ b/arch/arm/dts/ast2500-evb.dts
@@ -60,6 +60,10 @@
 	pinctrl-0 = <&pinctrl_mac2link_default &pinctrl_mdio2_default>;
 };
 
+&sdmmc {
+	status = "okay";
+};
+
 &sdhci0 {
 	status = "okay";