f2fs: Fix accounting for unusable blocks

Fixes possible underflows when dealing with unusable blocks.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Daniel Rosenberg 2019-05-29 17:49:05 -07:00 • committed by Jaegeuk Kim
commit a4c3ecaaad