Force HiFiBerry dacplus to slave mode temporarily.

Change-Id: I93aeb63f8abf6205c034baa983f401566c25e16d
Reviewed-on: https://tp-biosrd-v02/gerrit/80774
Reviewed-by: Jamess Huang(黃以民) <Jamess_Huang@asus.com>
Tested-by: Jamess Huang(黃以民) <Jamess_Huang@asus.com>

Author: Angus_Wang

arch/arm/boot/dts/overlays/hifiberry-dacplus-overlay.dts

@@ -35,6 +35,7 @@
 		hifiberry_dacplus: __overlay__ {
 			compatible = "hifiberry,hifiberry-dacplus";
 			i2s-controller = <&i2s>;
+			hifiberry-dacplus,slave;
 			status = "okay";
 		};
 	};