fix util import (#5542)

Author: zhyncs

python/sglang/srt/layers/quantization/fp8_utils.py

@@ -2,6 +2,8 @@
 
 import torch
 
+from sglang.srt.layers.quantization.fp8_kernel import sglang_per_token_group_quant_fp8
+
 try:
     from vllm import _custom_ops as vllm_ops