[Bugfix] DeepSeek V4: skip expert tensor when no mapping succeeds (AMD + NVIDIA)

[dparikh79]

What does this PR do?

DeepseekV4Model.load_weights in both vllm/models/deepseek_v4/nvidia/model.py and vllm/models/deepseek_v4/amd/model.py walks expert_mapping and assigns name_mapped inside the loop. When no entry matches (e.g. a quantization-specific layout like .tq_packed outside the standard gate_proj / up_proj / down_proj set), the loop falls through without binding name_mapped, and loaded_params.add(name_mapped) raises UnboundLocalError.

Track a success = False flag initialized before the loop and skip the add when no mapping succeeded. This also covers the silent-failure paths where a mapping does match but is_pp_missing_parameter or weight_loader returns False; those were previously appending a stale name_mapped from a different iteration. Shape matches the sibling deepseek_v4_mtp.py expert-loading path, which adds to loaded_params only inside the if success: branch.

After #43004 ([Model Refactoring] Migrate DeepSeek V4 to vllm/models/ [1/N]) the single vllm/model_executor/models/deepseek_v4.py file split into per-backend forks under vllm/models/deepseek_v4/{amd,nvidia}/model.py, and both forks carry the same buggy expert-loading block. The same fix is applied to both.

Replaces #42804 (against the pre-migration vllm/model_executor/models/deepseek_v4.py).

Closes #42769

Test Plan

• Existing DeepSeek V4 load_weights coverage via CI.

Duplicate-work check

gh pr list --repo vllm-project/vllm --state open --search "deepseek_v4 expert mapping name_mapped" returns nothing else for #42769. Pre-migration sibling #42804 is being closed in favor of this PR.

AI Assistance Disclosure

Drafted with Claude assistance. I am the human contributor accountable for this PR; I read every changed line, confirmed the AMD and NVIDIA forks carry byte-identical buggy blocks in the relevant region, and verified the if success: pattern matches the precedent in deepseek_v4_mtp.py.

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