Fix Device Index for ROCm Ray Workers in MoE Benchmark (#38108)

Signed-off-by: Liwen <53441624+li-liwen@users.noreply.github.com>
Co-authored-by: Kunshang Ji <kunshang.ji@intel.com>

benchmarks/kernels/benchmark_moe.py

@@ -627,9 +627,8 @@ class BenchmarkWorker:
                 need_device_guard = True
 
         with (
-            torch.accelerator.device_index(self.device_id)
-            if need_device_guard
-            else nullcontext()
+            # Ray restricts each worker to one GPU; use local index 0
+            torch.accelerator.device_index(0) if need_device_guard else nullcontext()
         ):
             for idx, config in enumerate(tqdm(search_space)):
                 try: