Documentation/devicetree/bindings/usb/dwc3-st.txt: update usb-drd.yaml reference

Changeset b0864e1a ("dt-bindings: usb: Convert generic USB properties to DT schemas")
renamed: Documentation/devicetree/bindings/usb/generic.txt
to: Documentation/devicetree/bindings/usb/usb-drd.yaml.

Update its cross-reference accordingly.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/43d5049a8ed688980bee12ecf18ef9937981de39.1610605373.git.mchehab+huawei@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/dwc3-st.txt

@@ -37,7 +37,7 @@ NB: The dr_mode property described in [1] is NOT optional for this driver, as th
 is "otg", which isn't supported by this SoC. Valid dr_mode values for dwc3-st are either "host"
 or "device".
 
-[1] Documentation/devicetree/bindings/usb/generic.txt
+[1] Documentation/devicetree/bindings/usb/usb-drd.yaml
 
 Example: