Fix for stochastic depth decay rule in the TimeSformer implementation

[atawari]

Fixing typo to correct the stochastic depth decay rule

What does this PR do?

Implementation of drop_path module in TimesformerLayer uses a constant config.drop_path as oppose to stochastic drop path as expected - see comments here and authors implementation here

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Who can review?

@amyeroberts

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[atawari]

tagging @amyeroberts as the change is in the vision module.

[amyeroberts]

Thanks for fixing!

[HuggingFaceDocBuilderDev]

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