[SCSI] sd: fix return value of sd_sync_cache()

sd_sync_cache() should return -errno on error, fix it.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 12e18bb..3dda77c 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -766,7 +766,9 @@
 			sd_print_sense_hdr(sdkp, &sshdr);
 	}
 
-	return res;
+	if (res)
+		return -EIO;
+	return 0;
 }
 
 static int sd_issue_flush(struct device *dev, sector_t *error_sector)