f2fs: recovery missing dot dentries in root directory

If f2fs was corrupted with missing dot dentries in root dirctory,
it needs to recover them after fsck.f2fs set F2FS_INLINE_DOTS flag
in directory inode when fsck.f2fs detects missing dot dentries.

Signed-off-by: Xue Liu <liuxueliu.liu@huawei.com>
Signed-off-by: Yong Sheng <shengyong1@huawei.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>