[Doc]Modify errors in the tutorial document(qwen2-audio-7b)

[MrZ20]

What this PR does / why we need it?

Modify errors in the tutorial document(qwen2-audio-7b)

• Fixes Deprecated Import: Updates the import of FlexibleArgumentParser from vllm.utils to vllm.utils.argparse_utils to address a deprecation warning and prevent future ImportError.

Related errors：

ImportError: cannot import name 'FlexibleArgumentParser' from 'vllm.utils' (/vllm-workspace/vllm/vllm/utils/__init__.py)

• Corrects Max Sequence Length: Changes the --max_model_len from 16384 to the model-supported 8192. This resolves the ValueError caused by exceeding the model's physical context window (max_position_embeddings).

Related errors：

Value error, User-specified max_model_len (16384) is greater than the derived max_model_len 
(max_position_embeddings=8192 or model_max_length=None in model's config.json). To allow overriding this maximum, set 
the env var VLLM_ALLOW_LONG_MAX_MODEL_LEN=1. VLLM_ALLOW_LONG_MAX_MODEL_LEN must be used with extreme 
caution. If the model uses relative position encoding (RoPE), positions exceeding derived_max_model_len lead to nan. If the 
model uses absolute position encoding, positions exceeding derived_max_model_len will cause a CUDA array out-of-bounds 
error. [type=value_error, input_value=ArgsKwargs((), {'model': ...rocessor_plugin': None}), input_type=ArgsKwargs]

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[gemini-code-assist]

Code Review

This pull request aims to correct errors in the Qwen2-Audio-7B tutorial document. The changes include fixing an import path, updating the max_model_len parameter value, and correcting the model identifier in a curl example. These changes improve the accuracy of the tutorial. I've identified one remaining issue in a command-line argument and provided a suggestion for a fix. Overall, this is a helpful documentation update.

[gemini-code-assist]

The command-line argument for setting the maximum model length should use a hyphen instead of an underscore. The correct argument is --max-model-len, not --max_model_len. Using an underscore will likely cause the argument to be unrecognized and the command to fail.

Suggested change

	--max_model_len 8192 \
	--max-model-len 8192 \

[github-actions]

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[MrZ20]

@wangxiyuan @Yikun It addresses several issues/corrections in the tutorial documentation for Qwen2-Audio-7B. Once confirmed, this PR is ready to be merged.