fix log err

Summary: Closes https://github.com/facebook/rocksdb/pull/2206

Differential Revision: D5054222

Pulled By: yiwu-arbug

fbshipit-source-id: d8742bda1bf3e76d7b68eeb86df4608031b5cbc8

db/db_impl_compaction_flush.cc

@@ -1157,8 +1157,8 @@ Status DBImpl::BackgroundFlush(bool* made_progress, JobContext* job_context,
         "Calling FlushMemTableToOutputFile with column "
         "family [%s], flush slots available %d, compaction slots allowed %d, "
         "compaction slots scheduled %d",
-        cfd->GetName().c_str(), immutable_db_options_.max_background_flushes,
+        cfd->GetName().c_str(), immutable_db_options_.max_background_flushes -
-        bg_flush_scheduled_, BGCompactionsAllowed() - bg_compaction_scheduled_);
+        bg_flush_scheduled_, BGCompactionsAllowed(), bg_compaction_scheduled_);
     status = FlushMemTableToOutputFile(cfd, mutable_cf_options, made_progress,
                                        job_context, log_buffer);
     if (cfd->Unref()) {