Fix redundant kernels in moe (#1428)

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Author: fzyzcjy

flashinfer/fused_moe/core.py

@@ -1006,15 +1006,15 @@ def trtllm_fp4_block_scale_moe_op(
 
         # workspace buffers required by trtllm-gen
         if topk_ids is None:
-            topk_ids = torch.zeros(
+            topk_ids = torch.empty(
                 num_tokens, top_k, dtype=torch.int32, device=hidden_states.device
             )
         if expert_weights is None:
-            expert_weights = torch.zeros(
+            expert_weights = torch.empty(
                 num_tokens, top_k, dtype=routing_dtype, device=hidden_states.device
             )
         if output is None:
-            output = torch.zeros(
+            output = torch.empty(
                 num_tokens,
                 hidden_size,
                 dtype=torch.bfloat16,