Fix Deepseek transformers model loading (#740)

## What does this PR do?

**Type of change:** ? Bug fix

**Overview:** ?
For Deepseek, let's force the user to apply trust_remote_code and use
AutoModelForCausalLM for loading the model.

## Testing
python hf_ptq.py --pyt_ckpt_path <Kimi-K2-Thinking_path> --qformat nvfp4
--export_path <quantized_ckpt> --kv_cache_qformat none --calib_size 64
--trust_remote_code --dataset cnn_dailymail

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## Additional Information
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Signed-off-by: Chenjie Luo <chenjiel@nvidia.com>

Author: cjluo-nv

examples/llm_ptq/example_utils.py

@@ -349,11 +349,12 @@ def get_model(
         else:
             architecture = hf_config.architectures[0]
 
-            if not hasattr(transformers, architecture):
-                warnings.warn(
-                    f"Architecture {architecture} not found in transformers: {transformers.__version__}. "
-                    "Falling back to AutoModelForCausalLM."
-                )
+            if not hasattr(transformers, architecture) or "Deepseek" in architecture:
+                if not hasattr(transformers, architecture):
+                    warnings.warn(
+                        f"Architecture {architecture} not found in transformers: {transformers.__version__}. "
+                        "Falling back to AutoModelForCausalLM."
+                    )
                 assert trust_remote_code, (
                     "Please set trust_remote_code to True if you want to use this architecture"
                 )