[RISCV][NFC] Update V spec section numbers

The section numbers got reshuffled around between v0.10 and [[ https://github.com/riscv/riscv-v-spec/blob/v1.0/v-spec.adoc |  v1.0 of the spec ]], this updates references in comments to refer to their version in v1.0.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D141382