Btrfs: check return value of btrfs_inc_extent_ref()

If return value of btrfs_inc_extent_ref() is not 0, BUG() is called.
Signed-off-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/tree-log.c

@@ -589,6 +589,7 @@ static noinline int replay_one_extent(struct btrfs_trans_handle *trans,
 						ins.objectid, ins.offset,
 						0, root->root_key.objectid,
 						key->objectid, offset);
+				BUG_ON(ret);
 			} else {
 				/*
 				 * insert the extent pointer in the extent