Summary:
Fix regression script for async_io benchmarks to report right ops/sec and latency

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11462

Test Plan: Verified locally

Reviewed By: anand1976

Differential Revision: D46031147

Pulled By: akankshamahajan15

fbshipit-source-id: 33ba587e6569ab2f834381ac2538e61da6876405