fix: Fix sorting buffer in clustering compaction (#38417)

issue: #28410

Signed-off-by: Cai Zhang <cai.zhang@zilliz.com>

internal/datanode/compaction/clustering_compactor.go

@@ -857,7 +857,7 @@ func (t *clusteringCompactionTask) flushLargestBuffers(ctx context.Context) erro
 		t.clusterBufferLocks.RUnlock(buffer.id)
 	}
 	sort.Slice(bufferIDs, func(i, j int) bool {
-		return bufferRowNums[i] > bufferRowNums[j]
+		return bufferRowNums[bufferIDs[i]] > bufferRowNums[bufferIDs[j]]
 	})
 	log.Info("start flushLargestBuffers", zap.Ints("bufferIDs", bufferIDs), zap.Int64("currentMemorySize", currentMemorySize))