ARM: dts: at_xdmac: fix bad value of dma-cells in documentation

The dma-cells value in the example was 2 instead of 1.
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

Documentation/devicetree/bindings/dma/atmel-xdma.txt

@@ -22,7 +22,7 @@ dma1: dma-controller@f0004000 {
 	compatible = "atmel,sama5d4-dma";
 	reg = <0xf0004000 0x200>;
 	interrupts = <50 4 0>;
-	#dma-cells = <2>;
+	#dma-cells = <1>;
 };