dt-bindings: mfd: rk808: update rockchip,rk808.yaml reference

Changeset 6c38ca03406e ("dt-bindings: mfd: rk808: Convert bindings to yaml")
renamed: Documentation/devicetree/bindings/mfd/rk808.txt
to: Documentation/devicetree/bindings/mfd/rockchip,rk808.yaml.

Update its cross-reference accordingly.

Fixes: 6c38ca03406e ("dt-bindings: mfd: rk808: Convert bindings to yaml")
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/pinctrl/pinctrl-rk805.txt

···
 - pins: List of pins. Valid values of pins properties are: gpio0, gpio1.
 
 First 2 properties must be added in the RK805 PMIC node, documented in
-Documentation/devicetree/bindings/mfd/rk808.txt
+Documentation/devicetree/bindings/mfd/rockchip,rk808.yaml
 
 Optional properties:
 -------------------