docs: dt: fix a broken reference to input.yaml

The old file was converted to yaml, but its reference was
still pointing to the old one.

Fixes: 7cef1079e3 ("dt-bindings: input: Add common input binding in json-schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt

@@ -164,7 +164,7 @@ Required properties:
 - compatible: should be:
               "fsl,imx8qxp-sc-key"
               followed by "fsl,imx-sc-key";
-- linux,keycodes: See Documentation/devicetree/bindings/input/keys.txt
+- linux,keycodes: See Documentation/devicetree/bindings/input/input.yaml
 
 Example (imx8qxp):
 -------------