dt-bindings: arm: Correct links to idle states definitions

The arm,idle-state DT bindings recently got converted to the json-schema,
but some links are still pointing to the old, non-existing, txt file. Let's
update the links to fix this.

Fixes: baac82fe ("dt-bindings: arm: Convert arm,idle-state binding to DT schema")
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/cpus.yaml

@@ -216,7 +216,7 @@ properties:
     $ref: '/schemas/types.yaml#/definitions/phandle-array'
     description: |
       List of phandles to idle state nodes supported
-      by this cpu (see ./idle-states.txt).
+      by this cpu (see ./idle-states.yaml).
 
   capacity-dmips-mhz:
     $ref: '/schemas/types.yaml#/definitions/uint32'