[clang] [llvm] [HLSL][SPRIV] Handle signed RWBuffer correctly (PR #144774)

[Steven Perron via cfe-commits]

s-perron wrote:

The failing spir-v test is caused by an update to spir-val (https://github.com/KhronosGroup/SPIRV-Tools/pull/6184), and is unrelated to this change.

https://github.com/llvm/llvm-project/pull/144774