[Minor] Change warning->warning_once in preprocess (vllm-project#26455)

Signed-off-by: Zhuohan Li <zhuohan123@gmail.com>
Signed-off-by: xuebwang-amd <xuebwang@amd.com>

Author: zhuohan123

vllm/inputs/preprocess.py

@@ -69,7 +69,7 @@ def get_tokenizer(self) -> AnyTokenizer:
 
     def get_bos_token_id(self) -> Optional[int]:
         if self.tokenizer is None:
-            logger.warning(
+            logger.warning_once(
                 "Using None for BOS token id because tokenizer is not initialized"
             )
             return None
@@ -78,7 +78,7 @@ def get_bos_token_id(self) -> Optional[int]:
 
     def get_eos_token_id(self) -> Optional[int]:
         if self.tokenizer is None:
-            logger.warning(
+            logger.warning_once(
                 "Using None for EOS token id because tokenizer is not initialized"
             )
             return None