correct pipeline class name (#5652)

Author: sayakpaul

src/diffusers/pipelines/pixart_alpha/pipeline_pixart_alpha.py

@@ -51,9 +51,7 @@
         >>> from diffusers import PixArtAlphaPipeline
 
         >>> # You can replace the checkpoint id with "PixArt-alpha/PixArt-XL-2-512x512" too.
-        >>> pipe = StableDiffusionXLPipeline.from_pretrained(
-        ...     "PixArt-alpha/PixArt-XL-2-1024-MS", torch_dtype=torch.float16
-        ... )
+        >>> pipe = PixArtAlphaPipeline.from_pretrained("PixArt-alpha/PixArt-XL-2-1024-MS", torch_dtype=torch.float16)
         >>> # Enable memory optimizations.
         >>> pipe.enable_model_cpu_offload()