dt-bindings: usb: aspeed: Remove the leading zeroes

Remove the leading zeroes to fix the following warning seen with
'make dt_binding_check':

Documentation/devicetree/bindings/usb/aspeed,usb-vhub.example.dts:37.33-42.23: Warning (unit_address_format): /example-0/usb-vhub@1e6a0000/vhub-strings/string@0409: unit name should not have leading 0s

Reviewed-by: Tao Ren <rentao.bupt@gmail.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20200629214027.16768-1-festevam@gmail.com
Signed-off-by: Rob Herring <robh@kernel.org>