Simple Cache Perftests: properly restore FD limit.

Fix typo in cache perftests.

BUG=none
R=jkarlin@chromium.org

Review-Url: https://codereview.chromium.org/2622013002
Cr-Commit-Position: refs/heads/master@{#442930}

net/disk_cache/disk_cache_perftest.cc

@@ -62,7 +62,7 @@ class DiskCachePerfTest : public DiskCacheTestWithCache {
 
   ~DiskCachePerfTest() override {
     if (saved_fd_limit_ < kFdLimitForCacheTests)
-      MaybeSetFdLimit(kFdLimitForCacheTests);
+      MaybeSetFdLimit(saved_fd_limit_);
   }
 
  protected: