GSD-2021-1000688 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 v4.9.271 by commit e934c4ee17b33bafb0444f2f9766cda7166d3c4...