fix: on-the-fly int4 quantize parameter (#1920)

Mirror to https://github.com/meta-llama/llama-models/pull/324 with some
clean up

```
with-proxy pip install -e .
export INFERENCE_MODEL=meta-llama/Llama-4-Scout-17B-16E-Instruct
export INFERENCE_CHECKPOINT_DIR=../checkpoints/Llama-4-Scout-17B-16E-Instruct
export QUANTIZATION_TYPE=int4_mixed
with-proxy llama stack build --run --template meta-reference-gpu
```

# What does this PR do?
[Provide a short summary of what this PR does and why. Link to relevant
issues if applicable.]

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan
[Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.*]

[//]: # (## Documentation)

llama_stack/models/llama/llama4/quantization/loader.py

@@ -91,7 +91,7 @@ def convert_to_quantized_model(
             log_status(f"Rank {rank}: Quantizing int4 weights from bf16")
 
             def apply_quantization(_, weight):
-                return quantize_int4(weight, fp8_activation_scale_ub, output_device=torch.device("cuda"))
+                return quantize_int4(weight, output_device=torch.device("cuda"))
 
     else:
         fp8_scales_path = os.path.join(checkpoint_dir, f"fp8_scales_{rank}.pt")