[SCSI] scsi_debug: fix false positive logical block reference tag check fail

Reading partially unwritten sectors generates a false positive logical
block reference tag check failure when DIF is enabled.

This bug is caused by missing ei_lba increment in loop of dif_verify()
when unwritten sector is skipped.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi_debug.c

@@ -1832,7 +1832,7 @@ static int prot_verify_read(struct scsi_cmnd *SCpnt, sector_t start_sec,
 	struct sd_dif_tuple *sdt;
 	sector_t sector;
 
-	for (i = 0; i < sectors; i++) {
+	for (i = 0; i < sectors; i++, ei_lba++) {
 		int ret;
 
 		sector = start_sec + i;
@@ -1846,8 +1846,6 @@ static int prot_verify_read(struct scsi_cmnd *SCpnt, sector_t start_sec,
 			dif_errors++;
 			return ret;
 		}
-
-		ei_lba++;
 	}
 
 	dif_copy_prot(SCpnt, start_sec, sectors, true);