btrfs-progs: use btrfs_lookup_block_group() in check_free_space_tree()

check_free_space_tree() is intended to check that the free-space tree
doesn't contain any entries which don't correspond to a block group.
Unfortunately it calls btrfs_lookup_first_block_group(), which only
returns NULL if the search offset is larger than the start of any block
group.

Fix check_free_space_tree() to use btrfs_lookup_block_group() as was
obviously intended, and fix fsck-tests/054-orphan-directory to get rid
of its spurious free-space entries that this now diagnoses.

Signed-off-by: Mark Harmstone <mark@harmstone.com>

Author: maharmstone

common/clear-cache.c

@@ -164,7 +164,7 @@ static int check_free_space_tree(struct btrfs_root *root)
 			goto out;
 		}
 
-		bg = btrfs_lookup_first_block_group(fs_info, key.objectid);
+		bg = btrfs_lookup_block_group(fs_info, key.objectid);
 		if (!bg) {
 			fprintf(stderr,
 		"We have a space info key for a block group that doesn't exist\n");