In fact, if the HBA's transfer_data callback goes on with scsi_req_continue
the request will be completed successfully instead of showing a failure.
It can even cause a segmentation fault.

An easy way to trigger it is "eject -f cd" during installation (during media
test if the installer does something like that).
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>