[model] fix qwen25vl config (#929)

### PR Category
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Serve

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| Performance | Breaking Change| Deprecations | Test Case | Docs |
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Bug Fixes

### PR Description
<!-- Describe what you’ve done -->
fix config about qwen2.5vl

Author: ceci3

examples/qwen2_5_vl/conf/serve/32b_instruct.yaml

@@ -8,8 +8,7 @@
     pipeline_parallel_size: 1
     max_num_seqs: 8 # Even at full 32,768 context usage, 8 concurrent operations won't trigger OOM
     gpu_memory_utilization: 0.9
-    limit_mm_per_prompt: image=18 # should be customized, 18 images/request is enough for most scenarios
+    limit_mm_per_prompt: '{"image": 18}' # should be customized, 18 images/request is enough for most scenarios
     port: 9010
     trust_remote_code: true
-    enforce_eager: true # better compare to FlagGems
     enable_chunked_prefill: true