ARM: dts: imx6qdl-gw551x: Do not use 'simple-audio-card,dai-link'

According to Documentation/devicetree/bindings/sound/simple-card.txt
the 'simple-audio-card,dai-link' may be omitted when the card has
only one DAI link, which is the case here.

Get rid of 'simple-audio-card,dai-link' in order to fix the following
build warning with W=1:

arch/arm/boot/dts/imx6qdl-gw551x.dtsi:109.32-121.5: Warning (unit_address_vs_reg): /sound-digital/simple-audio-card,dai-link@0: node has a unit name, but no reg property

Cc: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-gw551x.dtsi

@@ -105,19 +105,16 @@ reg_usb_otg_vbus: regulator-usb-otg-vbus {
 	sound-digital {
 		compatible = "simple-audio-card";
 		simple-audio-card,name = "tda1997x-audio";
+		simple-audio-card,format = "i2s";
+		simple-audio-card,bitclock-master = <&sound_codec>;
+		simple-audio-card,frame-master = <&sound_codec>;
 
-		simple-audio-card,dai-link@0 {
-			format = "i2s";
-
-			cpu {
-				sound-dai = <&ssi2>;
-			};
+		sound_cpu: simple-audio-card,cpu {
+			sound-dai = <&ssi2>;
+		};
 
-			codec {
-				bitclock-master;
-				frame-master;
-				sound-dai = <&hdmi_receiver>;
-			};
+		sound_codec: simple-audio-card,codec {
+			sound-dai = <&hdmi_receiver>;
 		};
 	};
 };