[llvm] [NFC][AMDGPU][Attributor] Only iterate over filtered functions when creating AAs (PR #108417)

[Shilei Tian via llvm-commits]

shiltian wrote:

> Weird that this SetVector is built in the first place

Well, my follow-up patch will use it soon. :-)

https://github.com/llvm/llvm-project/pull/108417