Opencode xfs-kill-xfs_dir_lookup_int here, which gets rid of a lock
roundtrip, and lots of stack space. Also kill the di_mode == 0 check that
has been done in xfs_iget for a few years now.

SGI-PV: 976035
SGI-Modid: xfs-linux-melb:xfs-kern:30901a
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>