[Community Pipeline] Fix typo that cause error on regional prompting pipeline (#10251)

fix: fix typo that cause error

examples/community/regional_prompting_stable_diffusion.py

@@ -129,7 +129,7 @@ class RegionalPromptingStableDiffusionPipeline(StableDiffusionPipeline):
         self.power = int(rp_args["power"]) if "power" in rp_args else 1
 
         prompts = prompt if isinstance(prompt, list) else [prompt]
-        n_prompts = negative_prompt if isinstance(prompt, list) else [negative_prompt]
+        n_prompts = negative_prompt if isinstance(negative_prompt, list) else [negative_prompt]
         self.batch = batch = num_images_per_prompt * len(prompts)
 
         if use_base: