xfs: prevent lockdep false positive in xfs_iget_cache_miss

The inode can't be locked by anyone else as we just created it a few
lines above and it's not been added to any lookup data structure yet.

So use a trylock that must succeed to get around the lockdep warnings.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Alexander Beregalov <a.beregalov@gmail.com>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Felix Blyakher <felixb@sgi.com>
Signed-off-by: Felix Blyakher <felixb@sgi.com>