fix sde add noise typo

[UranusITS]

What does this PR do?

Fixes typo of add_noise function in ScoreSdeVeScheduler.

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[patrickvonplaten]

Hey @UranusITS,

Could you run make style once to fix the code quality check?

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[patrickvonplaten]

Good job!