xfs: record inode buf errors as a xref error in inobt scrubber

xfs: record inode buf errors as a xref error in inobt scrubber

During the inode btree scrubs we try to confirm the freemask bits
against the inode records.  If the inode buffer read fails, this is a
cross-referencing error, not a corruption of the inode btree itself.
Use the xref_process_error call here.  Found via core.version middlebit
fuzz in xfs/415.

The userspace xfs_scrub program will try to repair outright corruptions
in the agi/inobt prior to phase 3 so that the inode scan will proceed.
If only a cross-referencing error is noted, the repair program defers
the repair attempt until it can check the other space metadata at least
once.

It is therefore essential that the inobt scrubber can correctly
distinguish between corruptions and "unable to cross-reference something
else with this inobt".

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>