use _make_causal_mask in clip/vit models
# What does this PR do?

Uses the `_make_causal_mask` helper to build the causal attention mask which works for `bfloat16` dtype.

the current `_build_causal_attention_mask` uses the `torch.triu_` which is not supported in pytorch release  fixed recently in main: https://github.com/pytorch/pytorch/pull/101414 

should fix https://github.com/huggingface/diffusers/issues/3453

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