[llvm] [DAGCombiner][NVPTX] Avoid forming illegal-typed shuffles after type-legalization (PR #205056)

[Thomas Raoux via llvm-commits]

https://github.com/ThomasRaoux approved this pull request.

The fix looks good to me, but it would be good to have a DAG selection expert look at it too

https://github.com/llvm/llvm-project/pull/205056