xfs: always grab transaction when scrubbing inode

Always allocate a transaction for inode scrubbing, even if the _iget
fails.  This is something that is nice to have now for consistency with
the other scrubbers but will become critical when we get to online
repair where we'll actually use the transaction + raw buffer read to fix
the verifier errors.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>