GSD-2021-1000537 btrfs: do not BUG_ON in link_to_fixup_dir

btrfs: do not BUGON in linktofixupdir This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.12.9 by commit b545442133580dcb2f2496133bf850824d41255c...