xfs: scrub should mark a directory corrupt if any entries cannot be iget'd

It's possible that xfs_iget can return EINVAL for inodes that the inobt
thinks are free, or ENOENT for inodes that look free.  If this is the
case, mark the directory corrupt immediately when we check ftype.  Note
that we already check the ftype of the '.' and '..' entries, so we
can skip the iget part since we already know the inode type for '.' and
we have a separate parent pointer scrubber for '..'.

Fixes: a5c46e5e ("xfs: scrub directory metadata")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>