cmd/go: fix proc-count accumulation in benchmark name

Fixes #14964

Change-Id: I5f772426081efaa9315c4ecaf60de850af324f1d
Reviewed-on: https://go-review.googlesource.com/21139Reviewed-by: Ahmed Waheed <oneofone@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/testing/benchmark.go

@@ -396,7 +396,7 @@ func (ctx *benchContext) processBench(b *B) {
 			b = &B{
 				common: common{
 					signal: make(chan bool),
-					name:   benchName,
+					name:   b.name,
 				},
 				benchFunc: b.benchFunc,
 				benchTime: b.benchTime,