UBI: add sanity check

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/scan.c b/drivers/mtd/ubi/scan.c
index 0c05f7b..e476638 100644
--- a/drivers/mtd/ubi/scan.c
+++ b/drivers/mtd/ubi/scan.c
@@ -286,9 +286,14 @@
 		 * FIXME: but this is anyway obsolete and will be removed at
 		 * some point.
 		 */
-
 		dbg_bld("using old crappy leb_ver stuff");
 
+		if (v1 == v2) {
+			ubi_err("PEB %d and PEB %d have the same version %lld",
+				seb->pnum, pnum, v1);
+			return -EINVAL;
+		}
+
 		abs = v1 - v2;
 		if (abs < 0)
 			abs = -abs;