unately, the stopped_td
and stopped_trb pointers were not getting cleared in this case.

The USB core unconditionally tries to reset the toggle bits on any
endpoints when a new alternate interface setting is installed.  When the
xHCI driver saw that ep->stopped_td was still set from the Stop Endpoint
command, xhci_reset_endpoint assumed the endpoint was actually stalled,
and attempted to clean up the endpoint rings.  This would manifest
itself in a failed Reset Endpoint command and failed Set TR dequeue
Pointer command after a successful Configure Endpoint command.  It may
have also been causing driver oops when the stopped_td was accessed.

This patch should be backported to stable kernels since 2.6.31.  Before
2.6.33, stopped_td was found in the xhci_endpoint_ring, not the
xhci_virt_ep.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
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