UBI: Fix error path in scan_pool()

We have to set "ret", not "err" in case of an error.
Reported-and-tested-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/ubi/fastmap.c

@@ -428,7 +428,7 @@ static int scan_pool(struct ubi_device *ubi, struct ubi_attach_info *ai,
 		if (be32_to_cpu(ech->image_seq) != ubi->image_seq) {
 			ubi_err("bad image seq: 0x%x, expected: 0x%x",
 				be32_to_cpu(ech->image_seq), ubi->image_seq);
-			err = UBI_BAD_FASTMAP;
+			ret = UBI_BAD_FASTMAP;
 			goto out;
 		}