fix HistogramWindowingImpl copy-{assignment,constructor}
fix HistogramWindowingImpl copy-{assignment,constructor}

Summary:
their arguments had a typo.
Closes https://github.com/facebook/rocksdb/pull/2821

Differential Revision: D5752408

Pulled By: ajkr

fbshipit-source-id: f2d84489c0c615b12a790f04c42d35cc0dccb02d

bbiao/rocksdb,bbiao/rocksdb,Andymic/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,Andymic/rocksdb,Andymic/rocksdb,Andymic/rocksdb,bbiao/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,bbiao/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb