[llvm] [RISCV] Fix masked->unmasked peephole handling masked pseudos with no passthru (PR #122253)

[Luke Lau via llvm-commits]

lukel97 wrote:

> I should do it in #115162. 😭

Looks like I reviewed it, and I didn't notice it either :)

https://github.com/llvm/llvm-project/pull/122253