xfs: fix iget usage in directory scrub [v24.5]

In this series, we fix some problems with how the directory scrubber
grabs child inodes.  First, we want to reduce EDEADLOCK returns by
replacing fixed-iteration loops with interruptible trylock loops.
Second, we add UNTRUSTED to the child iget call so that we can detect a
dirent that points to an unallocated inode.  Third, we fix a bug where
we weren't checking the inode pointed to by dotdot entries at all.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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