Fix implicit conversion between int64_t to int
Fix implicit conversion between int64_t to int

Summary:
Make conversion explicit, implicit conversion breaks the build
Closes https://github.com/facebook/rocksdb/pull/1589

Differential Revision: D4245158

Pulled By: IslamAbdelRahman

fbshipit-source-id: aaec00d

SunguckLee/RocksDB,SunguckLee/RocksDB,wat-ze-hex/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,vmx/rocksdb,vmx/rocksdb,vmx/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,Andymic/rocksdb,bbiao/rocksdb,bbiao/rocksdb,vmx/rocksdb,bbiao/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,vmx/rocksdb,bbiao/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,Andymic/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,Andymic/rocksdb,vmx/rocksdb