docs: dt: rockchip,dwc3.txt: fix a pointer to a renamed file

phy-rockchip-inno-usb2.txt was converted to yaml.

Fix the corresponding reference.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/usb/rockchip,dwc3.txt

@@ -16,7 +16,7 @@ A child node must exist to represent the core DWC3 IP block. The name of
 the node is not important. The content of the node is defined in dwc3.txt.
 
 Phy documentation is provided in the following places:
-Documentation/devicetree/bindings/phy/phy-rockchip-inno-usb2.txt - USB2.0 PHY
+Documentation/devicetree/bindings/phy/phy-rockchip-inno-usb2.yaml - USB2.0 PHY
 Documentation/devicetree/bindings/phy/phy-rockchip-typec.txt     - Type-C PHY
 
 Example device nodes: