GCC 8.x complains about improper usage of strncpy in virtio/net.c and
virtio/scsi.c:
In function 'virtio_scsi_init_one',
    inlined from 'virtio_scsi_init' at virtio/scsi.c:285:7:
virtio/scsi.c:247:2: error: 'strncpy' specified bound 224 equals destination size [-Werror=stringop-truncation]
  strncpy((char *)&sdev->target.vhost_wwpn, disk->wwpn, sizeof(sdev->target.vhost_wwpn));
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this and the other occurences in virtio/ by using strlcpy instead
of strncpy.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>