ASoC: dt-bindings: audio-graph-port: remove prefix

Audio Graph port doesn't use prefix.
This patch removes it.

Signed-off-by: Kuninori Morimoto <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

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

···
   port-base:
     $ref: /schemas/graph.yaml#/$defs/port-base
     properties:
-      prefix:
-        description: "device name prefix"
-        $ref: /schemas/types.yaml#/definitions/string
       convert-rate:
         $ref: "/schemas/sound/dai-params.yaml#/$defs/dai-sample-rate"
       convert-channels: