[llvm] [LV] Fix the cost of first order recurrence splice (PR #192473)

[Sander de Smalen via llvm-commits]

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sdesmalen-arm wrote:

Not that I can see, all paths that use the mask first check that it isn't empty, and most also only do this when the shuffleKind is `SK_Permute(Single|Two)Src`, not `SK_Splice`.

https://github.com/llvm/llvm-project/pull/192473