A deadlock can occur when the NFC raw socket is closed while
the driver is processing a command.

Following is the call graph of the affected situation:

send data via raw_sock:
-------------
rawsock_tx_work
  sock_hold => socket refcnt++
  nfc_data_exchange => cb = rawsock_data_exchange_complete

    ops->im_transceive = pn533_transceive => arg->cb = db
                               = rawsock_data_exchange_complete

      pn533_send_data_async => cb = pn533_data_exchange_complete

        __pn533_send_async => cmd->complete_cb = cb
                              = pn533_data_exchange_complete

          if_ops->send_frame_async

response:
--------
pn533_recv_response
  queue_work(priv->wq, &priv->cmd_complete_work)

pn533_wq_cmd_complete

  pn533_send_async_complete

    cmd->complete_cb() = pn533_data_exchange_complete()

      arg->cb() = rawsock_data_exchange_complete()

        sock_put => socket refcnt-- => If the corresponding
                    socket gets closed in the meantime socket
                    will be destructed

          sk_free

            __sk_free

              sk->sk_destruct = rawsock_destruct

                nfc_deactivate_target

                  ops->deactivate_target = pn533_deactivate_target

                    pn533_send_cmd_sync

                      pn533_send_cmd_async

                        __pn533_send_async

                          list_add_tail(&cmd->queue,&dev->cmd_queue)
                                  => add to command list because
                                     a command is currently
                                     processed

                        wait_for_completion
                                   => the workqueue thread waits
                                      here because it is the one
                                      processing the commands
                                         => deadlock

To fix the deadlock pn533_deactivate_target is changed to
issue the PN533_CMD_IN_RELEASE command in async mode. This
way nothing blocks and the release command is executed after
the current command.
Signed-off-by: Michael Thalmeier <michael.thalmeier@hale.at>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>