dt-bindings: usb: fix yamllint check warning

Fix warning: "missing starting space in comment"
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20210308053745.25697-1-chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/usb-device.yaml

@@ -82,9 +82,9 @@ required:
 additionalProperties: true
 
 examples:
-  #hub connected to port 1
-  #device connected to port 2
-  #device connected to port 3
+  # hub connected to port 1
+  # device connected to port 2
+  # device connected to port 3
   #    interface 0 of configuration 1
   #    interface 0 of configuration 2
   - |