[Bugfix] Fix FI kernel`chunk_gated_delta_rule` output shape for Qwen3.5 (#34219)

Signed-off-by: Roger Wang <hey@rogerw.io>

vllm/model_executor/models/qwen3_next.py

@@ -135,7 +135,7 @@ def fi_chunk_gated_delta_rule(
     fi_state = initial_state.to(torch.float32)
     fi_g = g.to(torch.float32)
     fi_beta = beta.to(torch.float32)
-    return chunk_gated_delta_rule_fi(
+    output, final_state = chunk_gated_delta_rule_fi(
         q=q,
         k=k,
         v=v,
@@ -145,6 +145,8 @@ def fi_chunk_gated_delta_rule(
         output_final_state=output_final_state,
         cu_seqlens=cu_seqlens,
     )
+    # Unsqueeze back to 4D (1, L, H, D) to match fla output format
+    return output.unsqueeze(0), final_state
 
 
 @CustomOp.register("chunk_gated_delta_rule")