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().
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>