f2fs: space related cleanup

Just for code style, no logic change
1. delete useless space
2. change spaces into tab

Signed-off-by: Jack Qiu <jack.qiu@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>