Update code example in pipeline_stable_unclip_img2img.py EXAMPLE_DOC_STRING (#8401)

Update code example in pipeline_stable_unclip_img2img.py

Previous code caused an error when run

src/diffusers/pipelines/stable_diffusion/pipeline_stable_unclip_img2img.py

@@ -51,8 +51,8 @@ EXAMPLE_DOC_STRING = """
         >>> from diffusers import StableUnCLIPImg2ImgPipeline
 
         >>> pipe = StableUnCLIPImg2ImgPipeline.from_pretrained(
-        ...     "fusing/stable-unclip-2-1-l-img2img", torch_dtype=torch.float16
-        ... )  # TODO update model path
+        ...     "stabilityai/stable-diffusion-2-1-unclip-small", torch_dtype=torch.float16
+        ... )
         >>> pipe = pipe.to("cuda")
 
         >>> url = "https://raw.githubusercontent.com/CompVis/stable-diffusion/main/assets/stable-samples/img2img/sketch-mountains-input.jpg"
@@ -63,7 +63,7 @@ EXAMPLE_DOC_STRING = """
 
         >>> prompt = "A fantasy landscape, trending on artstation"
 
-        >>> images = pipe(prompt, init_image).images
+        >>> images = pipe(init_image, prompt).images
         >>> images[0].save("fantasy_landscape.png")
         ```
 """