dt-bindings: soundwire: fix example

As wsa881x schema mentions #sound-dai-cells as required property,
so update soundwire-controller.yaml example so that dt_bindings_check
does not fail as below:

Documentation/devicetree/bindings/soundwire/soundwire-controller.example.dt.yaml:
speaker@0,1: '#sound-dai-cells' is a required property
Documentation/devicetree/bindings/soundwire/soundwire-controller.example.dt.yaml:
speaker@0,2: '#sound-dai-cells' is a required property

Reported-by: Rob Herring <[e-mail]>
Signed-off-by: Srinivas Kandagatla <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/soundwire/soundwire-controller.yaml

···
             reg = <0 1>;
             powerdown-gpios = <&wcdpinctrl 2 0>;
             #thermal-sensor-cells = <0>;
+            #sound-dai-cells = <0>;
         };
 
         speaker@0,2 {
···
             reg = <0 2>;
             powerdown-gpios = <&wcdpinctrl 2 0>;
             #thermal-sensor-cells = <0>;
+            #sound-dai-cells = <0>;
         };
     };