scsi: sym53c8xx_2: Use complete() instead complete_all()

There is only one waiter for the completion, therefore there is no need
to use complete_all(). Let's make that clear by using complete() instead
of complete_all().

The usage pattern of the completion is:

waiter context                          waker context

sym_eh_handler()
  struct completion eh_done
  init_completion(eh_done)
  pci_channel_offline()
  wait_for_completion_timeout(eh_done)

                                        sym2_io_resume()
                                          complete(eh_done)

Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>