cmd/pprof: fix scaling of "gigabyte" unit

Fixes #13654

Change-Id: Id2ce32c52efcfdbd66630725d62d2ca6bf0916d5
Reviewed-on: https://go-review.googlesource.com/17934
Reviewed-by: Russ Cox <[email protected]>

Author: bradfitz

src/cmd/pprof/internal/report/report.go

@@ -1505,7 +1505,7 @@ func memoryLabel(value int64, fromUnit, toUnit string) (v float64, u string, ok
 	case "megabyte", "mb":
 		value *= 1024 * 1024
 	case "gigabyte", "gb":
-		value *= 1024 * 1024
+		value *= 1024 * 1024 * 1024
 	default:
 		return 0, "", false
 	}