xfs: check for not fully initialized inodes in xfs_ireclaim

Add an assert for inodes not added to the inode cache in xfs_ireclaim,
to make sure we're not going to introduce something like the
famous nfsd inode cache bug again.

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