[llvm] [docs] Fix broken link in Benchmarking docs (PR #88117)

[Youngsuk Kim via llvm-commits]

JOE1994 wrote:

Test documentation build is failing due to error `"llvm/docs/Benchmarking.rst:14:Unexpected indentation.`.
I'll fix this before merging this PR..

https://github.com/llvm/llvm-project/pull/88117