[clang] [clang][CodeGen] `sret` args should always point to the `alloca` AS, so use that (PR #114062)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

@AlexVlx I found this breaks my clang build, reduced the C++ source to the following reproducer https://godbolt.org/z/jGnvKeqvr. Please verify that it breaks for you as well and revert or fix.

https://github.com/llvm/llvm-project/pull/114062