[llvm] [RISCV] Correct fcopysign pattern for zdinx (PR #114954)

[Sam Elliott via llvm-commits]

lenary wrote:

@futog Two quick notes:

- Please turn off [Keep my email addresses private](https://github.com/settings/emails) setting in your account - then I can merge your commit.

- Please don't force push, you can merge `main` into your branch if you need to (using a merge commit), rather than rebasing, if you need a later change from `main` on your branch. It should be fine now though.

https://github.com/llvm/llvm-project/pull/114954