mkfs: Add parent pointers during protofile creation

mkfs: Add parent pointers during protofile creation

Inodes created from protofile parsing will also need to add the
appropriate parent pointers.

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: use xfs_parent_add from libxfs instead of open-coding xfs_attr_set]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>