usb: core: unlink urbs from the tail of the endpoint's urb_list

While unlink an urb, if the urb has been programmed in the controller,
the controller driver might do some hw related actions to tear down the
urb.

Currently usb_hcd_flush_endpoint() passes each urb from the head of the
endpoint's urb_list to the controller driver, which could make the
controller driver think each urb has been programmed and take the
unnecessary actions for each urb.

This patch changes the behavior in usb_hcd_flush_endpoint() to pass the
urbs from the tail of the list, to avoid any unnecessary actions in an
controller driver.

Cc: stable@vger.kernel.org # v4.4+
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>