mfd: arizona: Correct link for sound binding document

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/mfd/arizona.txt

@@ -76,7 +76,7 @@ Deprecated properties:
 Also see child specific device properties:
   Regulator - ../regulator/arizona-regulator.txt
   Extcon    - ../extcon/extcon-arizona.txt
-  Sound     - ../sound/arizona.txt
+  Sound     - ../sound/wlf,arizona.txt
 
 Example: