[Bugfix] Fixes for new marlin moe usage (#18017)

Signed-off-by: mgoin <mgoin64@gmail.com>

vllm/model_executor/layers/quantization/gptq_marlin.py

@@ -610,9 +610,9 @@ class GPTQMarlinMoEMethod(FusedMoEMethodBase):
         activation: str = "silu",
     ) -> torch.Tensor:
         assert activation == "silu", "Only SiLU activation is supported."
-        if apply_router_weight_on_input is not None:
+        if apply_router_weight_on_input:
             raise NotImplementedError(
-                "Apply router weight on input is not supported for"
+                "Apply router weight on input is not supported for "
                 "fused Marlin MoE method.")
 
         topk_weights, topk_ids = FusedMoE.select_experts(