usb: wusbcore: prevent urb dequeue and giveback race

This patch takes a reference to the wa_xfer object in wa_urb_dequeue to
prevent the urb giveback code from completing the xfer and freeing it
while wa_urb_dequeue is executing.  It also checks for done at the start
to avoid a double completion scenario.  Adding the check for done in
urb_dequeue means that any other place where a submitted transfer
segment is marked as done must complete the transfer if it is done.
__wa_xfer_delayed_run was not checking this case so that check was added
as well.

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