compare_benchmark: fix ops/sec output.

The proper formula for a µs benchmark is not:

`time.Microsecond / cpuTimeUS`

but:

`time.Second / (cpuTimeUS * time.Microsecond)`

which simplifies to:

`(time.Second / time.Microsecond) / cpuTimeUS`

Change-Id: Ibec07cd968e44ea296175a4028f97a2b6a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/101227
Commit-Queue: Rudolf Polzer <rpolzer@google.com>
Reviewed-by: Xiangfei Ding <xfding@google.com>
Commit-Queue: Xiangfei Ding <xfding@google.com>
Auto-Submit: Rudolf Polzer <rpolzer@google.com>

util/compare_benchmarks.go

diff --git a/util/compare_benchmarks.go b/util/compare_benchmarks.go
index 867b0ef..eed190c 100644
--- a/util/compare_benchmarks.go
+++ b/util/compare_benchmarks.go
@@ -45,6 +45,7 @@
 	if r.BytesPerSecond != 0 {
 		return r.BytesPerSecond / 1000000, "MB/sec"
 	}
+
 	var unit time.Duration
 	switch r.TimeUnit {
 	case "ns":
@@ -56,7 +57,7 @@
 	default:
 		log.Panicf("unsupported time unit: %q", r.TimeUnit)
 	}
-	return float64(unit) / r.CPUTime, "ops/sec"
+	return float64(time.Second/unit) / r.CPUTime, "ops/sec"
 }
 
 func printResult(result Result, baseline *Result) error {