[Sparc] Fix instr desc of special register stores

- Those special register stores are STORE and their memory operands are
  input operands instead of output ones.

Reviewers:
JDevlieghere, arsenm, yinying-lisa-li, koachan, PeimingLiu, jyknight, aartbik, matthias-springer

Reviewed By: arsenm

Pull Request: https://github.com/llvm/llvm-project/pull/88971