[llvm] [SelectionDAG] Fix crash scalarizing `FLDEXP` with a legal `<1 x i1>` exponent (PR #224809)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

Is `<1 x float> @llvm.ldexp.v1f32.v1i1(<1 x float>, <1 x i1>)` a legal intrinsic? The [LangRef](https://llvm.org/docs/LangRef.html#llvm-ldexp-intrinsic) only illustrates the 2nd argument as i32. And v1i32 compiles without the change: https://godbolt.org/z/9bExeK81n

https://github.com/llvm/llvm-project/pull/224809