Cast height, width to int inside prepare latents

[DN6]

What does this PR do?

Originally proposed by @bghira in #7537. If float values are inadvertently passed in for height and width values in prepare_latents the pipeline throws an error. Explicitly cast height and width to int when preparing latents.

Opening this PR in order to resolve some merge conflicts in the original.

Fixes # (issue)

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[yiyixuxu]

thanks @bghira!