[Vision] fix small nit on `BeitDropPath` layers
# What does this PR do?

Fixes a small nit for `DropPath` layers pointed out in: https://github.com/huggingface/transformers/pull/20550#discussion_r1039395745 & https://github.com/huggingface/transformers/pull/20550#discussion_r1039459045 

Preferred to fix this separately in a PR to avoid modifying too much files in #20550

cc @NielsRogge @patrickvonplaten

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