[llvm] Fix Incorrect Tablegen Record for `S_CBRANCH_*_FORK` and `S_CBRANCH_JOIN` Instructions (PR #189205)

[Matin Raayai via llvm-commits]

matinraayai wrote:

> > * I would like to make the branches take quad SGPRs as implicit operands instead of single SGPRs, but I wasn't sure how to do that in tablegen.
> 
> Use the SReg_128 class as the operand type?

Is there an example in the backend that uses SReg_128 for defining register records? I've only seen the ones in the calling convention.

https://github.com/llvm/llvm-project/pull/189205