Btrfs: update comments in cache_save_setup

We also don't bother to flush free space cache while with free space
tree.

Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
1 file changed