Fix Tiling in `ConsistencyDecoderVAE`

[tolgacangoz]

Fixes #6126.

This pull request includes three commits:

• Fix tiling

• Add docstring to decode method in ConsistencyDecoderVAE

• Fix typos

I tested with this:

import torch
from diffusers import ConsistencyDecoderVAE

vae = ConsistencyDecoderVAE.from_pretrained("openai/consistency-decoder").to("cuda")
vae.enable_tiling()
vae.encode(torch.randn((1, 3, 256, 256), device="cuda"))

Also, this PR passes ./tests/models/autoencoders/test_models_vae.py tests in my local setup.

@yiyixuxu @sayakpaul