[llvm] Fix loop cache cost to avoid cost of zero for refgroups. (PR #88915)

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CongzheUalberta wrote:

Please squash your commits, and also update your commit messages to reflect your most recent changes (you are now rounding up the cost not only from 0 to 1). There's typo in your commit message as well (e.g., "stride"), please double check.

https://github.com/llvm/llvm-project/pull/88915