[spir-v, emit] Flat Decoration Adjustment

src/shader_recompiler/backend/spirv/spirv_emit_context.cpp

@@ -1463,8 +1463,10 @@ void EmitContext::DefineInputs(const IR::Program& program) {
         AddCapability(spv::Capability::GroupNonUniform);
         subgroup_local_invocation_id =
             DefineInput(*this, U32[1], false, spv::BuiltIn::SubgroupLocalInvocationId);
+        if (stage == Stage::Fragment) {
             Decorate(subgroup_local_invocation_id, spv::Decoration::Flat);
         }
+    }
     if (info.uses_fswzadd) {
         const Id f32_one{Const(1.0f)};
         const Id f32_minus_one{Const(-1.0f)};