Update autopipeline.md

[noelmateng]

Fixed incorrect reference to pipeline. The correct reference should be pipe_img2img.

What does this PR do?

Fix variable name inconsistency in Image-to-Image tutorial

In the Image-to-Image pipeline tutorial, there was a variable name mismatch that could cause confusion for users. The code was using pipeline instead of the previously defined pipe_img2img variable.

Changed:

• image = pipeline(prompt, image=init_image, generator=generator).images[0]

To:

• image = pipe_img2img(prompt, image=init_image, generator=generator).images[0]

This change ensures consistency with the pipeline initialization on the previous line:
pipe_img2img = AutoPipelineForImage2Image.from_pipe(pipe_txt2img).to("cuda")

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.