ASoC: dt-bindings: audio-graph-card2: reference audio-graph routing property

audio-graph.yaml already has "routing" property, let's reference it.

Signed-off-by: Kuninori Morimoto <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/audio-graph-card2.yaml

···
   label:
     maxItems: 1
   routing:
-    description: |
-      A list of the connections between audio components.
-      Each entry is a pair of strings, the first being the
-      connection's sink, the second being the connection's source.
-    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
+    $ref: audio-graph.yaml#/properties/routing
   aux-devs:
     description: |
       List of phandles pointing to auxiliary devices, such