[Bugfix] Fix unstable silu_mul+nvfp4 quant fusion test (#24370)

Signed-off-by: elvischenv <219235043+elvischenv@users.noreply.github.com>

tests/kernels/quantization/nvfp4_utils.py

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import torch
 
+from vllm._custom_ops import scaled_fp4_quant
 from vllm.scalar_type import scalar_types
 
 FLOAT4_E2M1_MAX = scalar_types.float4_e2m1f.max()
@@ -65,3 +66,10 @@ def break_fp4_bytes(a, dtype):
 
     # Reshape to final form
     return values.reshape(m, n * 2).to(dtype=dtype)
+
+
+def quant_nvfp4_tensor(a: torch.Tensor):
+    a_global_scale = ((FLOAT8_E4M3_MAX * FLOAT4_E2M1_MAX) /
+                      torch.abs(a).max().to(torch.float32))
+    a_quant, a_block_scale = scaled_fp4_quant(a, a_global_scale)
+    return a_quant, a_block_scale, a_global_scale