The probe gets an array subscript warning because gcc is not smart
enough to realise that a structure made up of multiple byte arrays
in it can be referenced as a flat buffer and it is valid to access
bytes beyond the first array in the structure....
Fix it by passing the adfs superblock in and using the internal
checksum array to get the checksum value.
Signed-off-by: Dave Chinner <david@fromorbit.com> Reviewed-by: Christoph Hellwig <hch@lst.de>