wusbcore: clean up list locking in urb enqueue

wa_urb_enqueue_run locks and unlocks its list lock as it traverses the
list of queued transfers.  This was done to prevent deadlocking due to
acquiring locks in reverse order in different places.  The problem is that
releasing the lock during the list traversal could allow the dequeue
routine to corrupt the list while it is being iterated over.  This patch
moves all list entries to a temp list while holding the list lock, then
traverses the temp list with no lock held.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>