[RISCV][CodeGen] Chapter of vector instruction type corresponds with chapters...

[RISCV][CodeGen] Chapter of vector instruction type corresponds with chapters in RISCV vector specification. NFC

The [vector spec](https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc) is organized in chapters
based on instruction type. The comments in the tablegen marked the incorrect chapters. This change
updates the comments with the correct chapter numbers.

Differential Revision: https://reviews.llvm.org/D138311