crypto-spec-scalar xperm4 xperm8 pseudo code fix

[dansmathers]

both xperm4 and xperm8 pseudo code show:
foreach(i from 0 to xlen by

but it should be

foreach(i from 0 to (xlen-1) by

e.g. for xperm8 in rv32, 0, 8, 16, 24. this is similar to what is currently checked in for the sail code.

[kdockser]

This change should be made to the Scalar Crypto spec. However, I don't know how such clarifications are to be made post-ratification. Does anyone know the policy on this?

[cetola]

Updates to ratified specifications should be noted in an errata folder, and updated in a revised publication of the specification. See the GitHub policy section containing "errata".

I'm going to work with Ken and Bill T to see that this gets updated.

Also, we will discuss this further on the documentation SIG if folks want to join in there.