[llvm] [AMDGPU][Attributor] Fix the merge of two range states of flat workgroup size (PR #125889)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> If we have a function `foo` that is called by two callers, `bar` and `baz`, where `bar` has `(32,256)` and `baz` has `(128,512)`, what should `foo` have?

`32, 512`. If you really wanted to increase the minimum range, you would have to modify the callers values too (which definitely isn't legal for the maximum, I'm less sure on the minimums)

https://github.com/llvm/llvm-project/pull/125889