Code review comment for ~raharper/curtin:fix/block-sfdisk-parsing

> Dan Watkins (daniel-thewatkins) wrote on 2020-05-04:
> Should we be raising this error in all the other places that we're using sfdisk_info?

For block-meta, I'll move this check to partition_verify which is the entry to
the verify partition code paths. We then pass the asserted value info to the
sub functions which will reuse this info without a second invocation.