The value of FAULT_* macros and its description in f2fs.rst became
inconsistent, fix this to keep compatibility of fault injection
interface.

Fixes: 67883ade ("f2fs: remove FAULT_ALLOC_BIO")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>