update output for Hidream transformer (#11366)

up

Author: yiyixuxu

src/diffusers/models/transformers/transformer_hidream_image.py

@@ -918,5 +918,5 @@ def forward(
             unscale_lora_layers(self, lora_scale)
 
         if not return_dict:
-            return (output, hidden_states_masks)
-        return Transformer2DModelOutput(sample=output, mask=hidden_states_masks)
+            return (output,)
+        return Transformer2DModelOutput(sample=output)