[llvm] [SelectionDAG][RISCV] Fix break of vnsrl pattern in issue #94265 (PR #95563)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

This breaks a number of tests:
```
Failed Tests (8):
  LLVM :: CodeGen/AArch64/bitfield-extract.ll
  LLVM :: CodeGen/AArch64/extbinopload.ll
  LLVM :: CodeGen/AArch64/trunc-to-tbl.ll
  LLVM :: CodeGen/AArch64/zext-to-tbl.ll
  LLVM :: CodeGen/AMDGPU/amdgpu-codegenprepare-idiv.ll
  LLVM :: CodeGen/Hexagon/two-crash.ll
  LLVM :: CodeGen/Thumb2/shift_parts.ll
  LLVM :: CodeGen/X86/pr44915.ll
```

https://github.com/llvm/llvm-project/pull/95563