[llvm] [RISCV][Disassemble] Ensure the comment stream of the disassembler is set. (PR #125962)

[Francesco Petrogalli via llvm-commits]

fpetrogalli wrote:

> Maybe we just need to set the comment stream in HexagonDisassembler::getInstruction?

Or maybe just revert my commit and https://github.com/llvm/llvm-project/commit/1ea5ce6335c7c0e040f70de16f1080546d242b69 and get back to the assumption that the comment stream might be null?

https://github.com/llvm/llvm-project/pull/125962