benchmark: fix off-by-one error in fs benchmarks

Fix a off-by-one error that made the benchmarks for asynchronous
functions run `n - 1` times instead of `n` times.

PR-URL: https://github.com/nodejs/node/pull/8338
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

benchmark/fs/bench-readdir.js

@@ -14,7 +14,7 @@ function main(conf) {
 
   bench.start();
   (function r(cntr) {
-    if (--cntr <= 0)
+    if (cntr-- <= 0)
       return bench.end(n);
     fs.readdir(path.resolve(__dirname, '../../lib/'), function() {
       r(cntr);

benchmark/fs/bench-realpath.js

@@ -27,7 +27,7 @@ function main(conf) {
 
 function relativePath(n) {
   (function r(cntr) {
-    if (--cntr <= 0)
+    if (cntr-- <= 0)
       return bench.end(n);
     fs.realpath(relative_path, function() {
       r(cntr);
@@ -37,7 +37,7 @@ function relativePath(n) {
 
 function resolvedPath(n) {
   (function r(cntr) {
-    if (--cntr <= 0)
+    if (cntr-- <= 0)
       return bench.end(n);
     fs.realpath(resolved_path, function() {
       r(cntr);