btrfs: open code btrfs_backref_iter_free()

The helper is trivial and used only once, open code it. It's safe to
remove the 'if', the pointer is validated in build_backref_tree().
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.h

@@ -283,14 +283,6 @@ struct btrfs_backref_iter {
 
 struct btrfs_backref_iter *btrfs_backref_iter_alloc(struct btrfs_fs_info *fs_info);
 
-static inline void btrfs_backref_iter_free(struct btrfs_backref_iter *iter)
-{
-	if (!iter)
-		return;
-	btrfs_free_path(iter->path);
-	kfree(iter);
-}
-
 static inline struct extent_buffer *btrfs_backref_get_eb(
 		struct btrfs_backref_iter *iter)
 {

fs/btrfs/relocation.c

@@ -523,7 +523,8 @@ static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
 	if (handle_useless_nodes(rc, node))
 		node = NULL;
 out:
-	btrfs_backref_iter_free(iter);
+	btrfs_free_path(iter->path);
+	kfree(iter);
 	btrfs_free_path(path);
 	if (err) {
 		btrfs_backref_error_cleanup(cache, node);