btrfs: prepare btrfs_launcher_folio() for large folios support

That function is only calling btrfs_qgroup_free_data(), which doesn't
care about the size of the folio.

Just replace the fixed PAGE_SIZE with folio_size().

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>