Btrfs: remove dead code

merge is always NULL at this point.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/extent_map.c

@@ -234,7 +234,6 @@ int add_extent_mapping(struct extent_map_tree *tree,
 	rb = tree_insert(&tree->map, em->start, &em->rb_node);
 	if (rb) {
 		ret = -EEXIST;
-		free_extent_map(merge);
 		goto out;
 	}
 	atomic_inc(&em->refs);