scsi: xen: Drop use of internal host codes

The error codes:

 - DID_TARGET_FAILURE

 - DID_NEXUS_FAILURE

 - DID_ALLOC_FAILURE

 - DID_MEDIUM_ERROR

are internal to the SCSI layer. Drivers must not use them because:

 1. They are not propagated upwards, so SG IO/passthrough users will not
    see an error and think a command was successful.

    xen-scsiback will never see this error and should not try to send it.

 2. There is no handling for them in scsi_decide_disposition() so if
    xen-scsifront were to return the error to the SCSI midlayer then it
    kicks off the error handler which is definitely not what we want.

Remove the use from xen-scsifront/back.

Link: https://lore.kernel.org/r/20220812010027.8251-2-michael.christie@oracle.com


Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>