[Docs] Fix stable_diffusion.mdx typo (huggingface#3398)

Fix typo in last code block. Correct "prommpts" to "prompt"

Author: sudowind

docs/source/en/stable_diffusion.mdx

@@ -246,7 +246,7 @@ image_grid(images, rows=2, cols=4)
 Pretty impressive! Let's tweak the second image - corresponding to the `Generator` with a seed of `1` - a bit more by adding some text about the age of the subject:
 
 ```python
-prommpts = [
+prompts = [
     "portrait photo of the oldest warrior chief, tribal panther make up, blue on red, side profile, looking away, serious eyes 50mm portrait photography, hard rim lighting photography--beta --ar 2:3  --beta --upbeta",
     "portrait photo of a old warrior chief, tribal panther make up, blue on red, side profile, looking away, serious eyes 50mm portrait photography, hard rim lighting photography--beta --ar 2:3  --beta --upbeta",
     "portrait photo of a warrior chief, tribal panther make up, blue on red, side profile, looking away, serious eyes 50mm portrait photography, hard rim lighting photography--beta --ar 2:3  --beta --upbeta",