Fix MMAudio TypeError: cast num_steps to int in _mmaudio_gpu_infer

FlowMatching(num_steps=num_steps) was receiving a string from Gradio,
causing 'can only concatenate str (not int) to str' in torch.linspace.
Add int(num_steps) cast alongside the existing num_samples/crossfade_s casts.

app.py

@@ -1054,6 +1054,7 @@ def _mmaudio_gpu_infer(video_file, prompt, negative_prompt, seed_val,
 
     seed_val     = _resolve_seed(seed_val)
     num_samples  = int(num_samples)
+    num_steps    = int(num_steps)
     crossfade_s  = float(crossfade_s)
 
     device, dtype = _get_device_and_dtype()