[docs] typo : corrected 'compile regions' to 'compile_regions'

[Manith-Ratnayake]

What does this PR do?

Fixes a small typo in the documentation example
(Source: https://huggingface.co/docs/diffusers/en/optimization/fp16)

# pip install -U accelerate
import torch
from diffusers import StableDiffusionXLPipeline
from accelerate.utils import compile regions

pipeline = StableDiffusionXLPipeline.from_pretrained(
    "stabilityai/stable-diffusion-xl-base-1.0", torch_dtype=torch.float16
).to("cuda")
pipeline.unet = compile_regions(pipeline.unet, mode="reduce-overhead", fullgraph=True)

There is a small typo in this line

from accelerate.utils import compile regions

I added an underscore between the word compile and regions to fix it

from accelerate.utils import compile_regions

This makes the import syntax correct and allows the example to run properly.

pipeline.unet = compile_regions(pipeline.unet, mode="reduce-overhead", fullgraph=True)