[Bugfix] Fix incorrect image_grid_thw rank for HunyuanOCR from missing merge_by_field_config=True (#29950)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>

vllm/model_executor/models/hunyuan_vision.py

@@ -785,6 +785,7 @@ class HunYuanVLForConditionalGeneration(
     SupportsQuant,
     SupportsXDRoPE,
 ):
+    merge_by_field_config = True
     multimodal_cpu_fields = {"image_grid_thw"}
 
     # To ensure correct weight loading and mapping.