btrfs: don't use WARN_ON when ret is -ENOTENT in __btrfs_free_extent()

hulk inclusion
category: bugfix
bugzilla: 13690
CVE: CVE-2019-19039

-------------------------------------------------

Avoid print register messages when ret is -ENOTENT.
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/btrfs/extent-tree.c

@@ -6793,7 +6793,7 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
 			}
 			extent_slot = path->slots[0];
 		}
-	} else if (WARN_ON(ret == -ENOENT)) {
+	} else if (ret == -ENOENT) {
 		btrfs_print_leaf(path->nodes[0]);
 		btrfs_err(info,
 			"unable to find ref byte nr %llu parent %llu root %llu  owner %llu offset %llu",