Use lookup_one_len instead of opencoding a simplified lookup using
lookup_hash with a fake hash.

Also there's no need anymore for the d_invalidate as we have a completely
valid dentry now.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>