Make sure to call into the USB core's link, unlink, and giveback URB
functions with the usb_hcd pointer found by using urb->dev->bus. This
will avoid confusion later, when the xHCI driver will deal with URBs from
two separate buses (the USB 3.0 roothub and the faked USB 2.0 roothub).
Assume xhci_urb_dequeue() will be called with the proper usb_hcd.
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
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