f2fs: Create COW inode from parent dentry for atomic write

f2fs: Create COW inode from parent dentry for atomic write

The i_pino in f2fs_inode_info has the previous parent's i_ino when inode
was renamed, which may cause f2fs_ioc_start_atomic_write to fail.
If file_wrong_pino is true and i_nlink is 1, then to find a valid pino,
we should refer to the dentry from inode.

To resolve this issue, let's get parent inode using parent dentry
directly.

Fixes: 3db1de0e582c ("f2fs: change the current atomic write way")
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>
Reviewed-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>