[SCSI] scsi_debug: fix duplicate dif_errors increment

It is unnecessary to increase dif_errors in dif_verify(), because the
caller will increment it when dif_verify() detects failure.

This bug was introduced by commit beb40ea4 ("[SCSI] scsi_debug:
reduce duplication between prot_verify_read and prot_verify_write")
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

@@ -1780,7 +1780,6 @@ static int dif_verify(struct sd_dif_tuple *sdt, const void *data,
 	    be32_to_cpu(sdt->ref_tag) != ei_lba) {
 		pr_err("%s: REF check failed on sector %lu\n",
 			__func__, (unsigned long)sector);
-			dif_errors++;
 		return 0x03;
 	}
 	return 0;