[llvm] Fix dead link to paper in benchmarking documentation. (PR #69645)

[Shivam Gupta via llvm-commits]

xgupta wrote:

This is actually fix/committed via https://github.com/llvm/llvm-project/pull/88117. 
So we can close this PR, thank @sashafrolov.

https://github.com/llvm/llvm-project/pull/69645