dt-bindings: dma: uart: mtk: fix example

The binding example is missing the fallback compatible.
This is needed as the driver only matches against mt6577.
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/dma/mtk-uart-apdma.txt

@@ -21,7 +21,8 @@ Required properties:
 Examples:
 
 	apdma: dma-controller@11000400 {
-		compatible = "mediatek,mt2712-uart-dma";
+		compatible = "mediatek,mt2712-uart-dma",
+			     "mediatek,mt6577-uart-dma";
 		reg = <0 0x11000400 0 0x80>,
 		      <0 0x11000480 0 0x80>,
 		      <0 0x11000500 0 0x80>,