scsi: virtio_scsi: 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

virtscsi_tmf()
  DECLARE_COMPLETION_ONSTACK()
  virtscsi_kick_cmd()
  wait_for_completion()

                                        virtscsi_complete_free()
                                          complete()
Signed-off-by: NDaniel Wagner <daniel.wagner@bmw-carit.de>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/virtio_scsi.c

@@ -258,7 +258,7 @@ static void virtscsi_complete_free(struct virtio_scsi *vscsi, void *buf)
 	struct virtio_scsi_cmd *cmd = buf;
 
 	if (cmd->comp)
-		complete_all(cmd->comp);
+		complete(cmd->comp);
 }
 
 static void virtscsi_ctrl_done(struct virtqueue *vq)