xfs: pass an on-disk extent to xfs_bmbt_validate_extent

This prepares for getting rid of the current in-memory extent format.
At the end of the series we will change the calling convention again
to pass the xfs_bmbt_irec structure once it is available everywhere.

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