Fix a wrong log formatting
Fix a wrong log formatting

Summary:
I experienced weird segfault because of this mismatch of type in log formatting. Fix it.
Closes https://github.com/facebook/rocksdb/pull/3345

Differential Revision: D6687224

Pulled By: siying

fbshipit-source-id: c51fb1c008b7ebc3efdc353a4adad3e8f5b3e9de

SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB,SunguckLee/RocksDB