sc58x: correct mmc clock assignment in device tree

Previously the incorrect clock was listed, resulting in a
larger-than-necessary divisor being selected, leading to reduced mmc
performance. This changes the clock configuration to match the
configuration listed in the linux device tree and improves measured
read/write speeds

arch/arm/dts/sc58x.dtsi

@@ -127,7 +127,7 @@
 };
 
 &mmc{
-	clocks = <&dummy>, <&clk ADSP_SC58X_CLK_CGU0_SCLK0>;
+	clocks = <&clk ADSP_SC58X_CLK_CGU0_SCLK0>, <&clk ADSP_SC58X_CLK_SDIO>;
 };
 
 &i2c0{