[llvm] [TableGen] Bug fix for tied optional operands resolution (PR #83588)

[Sergei Barannikov via llvm-commits]

https://github.com/s-barannikov approved this pull request.

Could you add a FIXME near OpIdx calculation that it is not an operand index in CVT_Tied case?

https://github.com/llvm/llvm-project/pull/83588