fsck.f2fs: fix incorrect parent blkaddr when adding lost dots

If dot or dotdot is lost, fsck tries to add a new dentry by
f2fs_add_link(). The blkaddr of the directory inode should be
passed to it in order to update the dirty inode at the right
place. This patch fixes the uninitialized `blkaddr' to avoid
corrupting f2fs image.

Signed-off-by: Sheng Yong <shengyong@oppo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>