[Chore] Adjust tokenizer import to avoid circular imports (#30601)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

benchmarks/backend_request_func.py

@@ -620,7 +620,7 @@ def get_tokenizer(
         kwargs["use_fast"] = False
     if tokenizer_mode == "mistral":
         try:
-            from vllm.tokenizers import MistralTokenizer
+            from vllm.tokenizers.mistral import MistralTokenizer
         except ImportError as e:
             raise ImportError(
                 "MistralTokenizer requires vllm package.\n"