[llvm] [SPIRV] Update the global registry when expanding function pointer (PR #183873)

[Juan Manuel Martinez Caamaño via llvm-commits]

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jmmartinez wrote:

To fix the failing test, it seems there was a use of the old `NewReg` that is missing an update.
```suggestion
              .addDef(ResVReg)
```

https://github.com/llvm/llvm-project/pull/183873