[SCSI] Retry ADD_TO_MLQUEUE return value for EH commands

A target reset when I/O is ongoing might result
an eventual device offline, as scsi_eh_completed_normally()
might return ADD_TO_MLQUEUE in addition to the
advertised SUCCESS, FAILED, and NEEDS_RETRY.

Which is unfortunate as scsi_send_eh_cmnd() will
therefore map ADD_TO_MLQUEUE to FAILED instead of
the more appropriate NEEDS_RETRY.
Signed-off-by: Hannes Reinecke <hare@suse.de>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/scsi_error.c

@@ -725,6 +725,9 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
 		case NEEDS_RETRY:
 		case FAILED:
 			break;
+		case ADD_TO_MLQUEUE:
+			rtn = NEEDS_RETRY;
+			break;
 		default:
 			rtn = FAILED;
 			break;