xfs: tell lockdep about parent iolock usage in filestreams

The filestreams code may take the iolock on the parent inode while
holding it on a child.  This is the only place in XFS where we take
both the child and parent iolock, so just telling lockdep about it
is enough.  The lock flag required for that was already added as
part of the ilock lockdep annotations and unused so far.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>