fix small mistake in annotation: 32 -> 64 (huggingface#1780)

Fix inconsistencies between code and comments in the function 'preprocess'

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_upscale.py

@@ -39,7 +39,7 @@ def preprocess(image):
 
     if isinstance(image[0], PIL.Image.Image):
         w, h = image[0].size
-        w, h = map(lambda x: x - x % 64, (w, h))  # resize to integer multiple of 32
+        w, h = map(lambda x: x - x % 64, (w, h))  # resize to integer multiple of 64
 
         image = [np.array(i.resize((w, h)))[None, :] for i in image]
         image = np.concatenate(image, axis=0)