ASoC: audio-graph-card: update audio-graph-card.yaml reference

Changeset 97198614 ("ASoC: audio-graph-card: switch to yaml base Documentation")
renamed: Documentation/devicetree/bindings/sound/audio-graph-card.txt
to: Documentation/devicetree/bindings/sound/audio-graph-card.yaml.

Update its cross-reference accordingly.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/8a779e6b9644d19c5d77b382059f6ccf9781434d.1610535350.git.mchehab+huawei@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/bridge/sii902x.txt

@@ -40,7 +40,7 @@ Optional properties:
 	documents on how to describe the way the sii902x device is
 	connected to the rest of the audio system:
 	Documentation/devicetree/bindings/sound/simple-card.yaml
-	Documentation/devicetree/bindings/sound/audio-graph-card.txt
+	Documentation/devicetree/bindings/sound/audio-graph-card.yaml
 	Note: In case of the audio-graph-card binding the used port
 	index should be 3.