f2fs: optimize error handling in redirty_blocks

Current error handling is at risk of page leaks. However, we dot't seek
any failure scenarios, just use f2fs_bug_on.

Signed-off-by: Jack Qiu <jack.qiu@huawei.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>