UBI: fix out of bounds write

If aeb->len >= vol->reserved_pebs, we should not be writing aeb into the
PEB->LEB mapping.

Caught by Coverity, CID #711212.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/eba.c

@@ -1419,7 +1419,8 @@ int ubi_eba_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
 				 * during re-size.
 				 */
 				ubi_move_aeb_to_list(av, aeb, &ai->erase);
-			vol->eba_tbl[aeb->lnum] = aeb->pnum;
+			else
+				vol->eba_tbl[aeb->lnum] = aeb->pnum;
 		}
 	}