ASoC: sgtl5000: Add audio-graph-card port

The SGTL5000 codec can be connected via audio-graph-card,
add the missing port: entry into the bindings.

Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20210610150135.29905-1-marex@denx.de
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/sgtl5000.yaml

@@ -75,6 +75,10 @@ properties:
     $ref: "/schemas/types.yaml#/definitions/uint32"
     enum: [ 0, 1, 2, 3 ]
 
+  port:
+    $ref: audio-graph-port.yaml#
+    unevaluatedProperties: false
+
 required:
   - compatible
   - reg