Tiny fix to db_bench for make release.
Tiny fix to db_bench for make release.

Summary:
In release, "found variable assigned but not used anywhere". Changed it to work with
assert. Someone accept this :).

Test Plan: make release -j 32

Reviewers: haobo, dhruba, emayanke

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D12309

NickCis/rocksdb,geraldoandradee/rocksdb,ryneli/rocksdb,amyvmiwei/rocksdb,vashstorm/rocksdb,Applied-Duality/rocksdb,virtdb/rocksdb,Andymic/rocksdb,rDSN-Projects/rocksdb.replicated,facebook/rocksdb,msb-at-yahoo/rocksdb,Applied-Duality/rocksdb,geraldoandradee/rocksdb,caijieming-baidu/rocksdb,NickCis/rocksdb,JoeWoo/rocksdb,norton/rocksdb,JackLian/rocksdb,hobinyoon/rocksdb,tizzybec/rocksdb,mbarbon/rocksdb,fengshao0907/rocksdb,ryneli/rocksdb,bbiao/rocksdb,luckywhu/rocksdb,fengshao0907/rocksdb,IMCG/RcoksDB,anagav/rocksdb,siddhartharay007/rocksdb,virtdb/rocksdb,caijieming-baidu/rocksdb,tizzybec/rocksdb,JoeWoo/rocksdb,tsheasha/rocksdb,biddyweb/rocksdb,rDSN-Projects/rocksdb.replicated,Andymic/rocksdb,wlqGit/rocksdb,geraldoandradee/rocksdb,flabby/rocksdb,tschottdorf/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,IMCG/RcoksDB,norton/rocksdb,vmx/rocksdb,OverlordQ/rocksdb,msb-at-yahoo/rocksdb,virtdb/rocksdb,Vaisman/rocksdb,facebook/rocksdb,bbiao/rocksdb,fengshao0907/rocksdb,wskplho/rocksdb,biddyweb/rocksdb,siddhartharay007/rocksdb,zhangpng/rocksdb,vashstorm/rocksdb,sorphi/rocksdb,jalexanderqed/rocksdb,Applied-Duality/rocksdb,ylong/rocksdb,kaschaeffer/rocksdb,flabby/rocksdb,mbarbon/rocksdb,facebook/rocksdb,wlqGit/rocksdb,siddhartharay007/rocksdb,skunkwerks/rocksdb,fengshao0907/rocksdb,JohnPJenkins/rocksdb,Vaisman/rocksdb,JackLian/rocksdb,JohnPJenkins/rocksdb,fengshao0907/rocksdb,makelivedotnet/rocksdb,wat-ze-hex/rocksdb,amyvmiwei/rocksdb,wat-ze-hex/rocksdb,JohnPJenkins/rocksdb,skunkwerks/rocksdb,vmx/rocksdb,vashstorm/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,JoeWoo/rocksdb,flabby/rocksdb,jalexanderqed/rocksdb,RyanTech/rocksdb,NickCis/rocksdb,caijieming-baidu/rocksdb,JoeWoo/rocksdb,luckywhu/rocksdb,hobinyoon/rocksdb,luckywhu/rocksdb,zhangpng/rocksdb,SunguckLee/RocksDB,kaschaeffer/rocksdb,fengshao0907/rocksdb,rDSN-Projects/rocksdb.replicated,vmx/rocksdb,dkorolev/rocksdb,ryneli/rocksdb,caijieming-baidu/rocksdb,temicai/rocksdb,norton/rocksdb,zhangpng/rocksdb,ylong/rocksdb,sorphi/rocksdb,tschottdorf/rocksdb,ylong/rocksdb,jalexanderqed/rocksdb,hobinyoon/rocksdb,bbiao/rocksdb,vmx/rocksdb,NickCis/rocksdb,ryneli/rocksdb,lgscofield/rocksdb,alihalabyah/rocksdb,Applied-Duality/rocksdb,vashstorm/rocksdb,bbiao/rocksdb,ryneli/rocksdb,sorphi/rocksdb,wat-ze-hex/rocksdb,amyvmiwei/rocksdb,virtdb/rocksdb,Andymic/rocksdb,hobinyoon/rocksdb,hobinyoon/rocksdb,biddyweb/rocksdb,wskplho/rocksdb,wskplho/rocksdb,bbiao/rocksdb,wskplho/rocksdb,anagav/rocksdb,NickCis/rocksdb,RyanTech/rocksdb,Vaisman/rocksdb,tsheasha/rocksdb,caijieming-baidu/rocksdb,JackLian/rocksdb,skunkwerks/rocksdb,virtdb/rocksdb,msb-at-yahoo/rocksdb,JackLian/rocksdb,biddyweb/rocksdb,flabby/rocksdb,zhangpng/rocksdb,OverlordQ/rocksdb,alihalabyah/rocksdb,vmx/rocksdb,norton/rocksdb,alihalabyah/rocksdb,msb-at-yahoo/rocksdb,tschottdorf/rocksdb,SunguckLee/RocksDB,flabby/rocksdb,mbarbon/rocksdb,makelivedotnet/rocksdb,skunkwerks/rocksdb,norton/rocksdb,lgscofield/rocksdb,tsheasha/rocksdb,wat-ze-hex/rocksdb,ylong/rocksdb,wat-ze-hex/rocksdb,luckywhu/rocksdb,JackLian/rocksdb,alihalabyah/rocksdb,wenduo/rocksdb,dkorolev/rocksdb,RyanTech/rocksdb,Vaisman/rocksdb,wenduo/rocksdb,vmx/rocksdb,geraldoandradee/rocksdb,facebook/rocksdb,wenduo/rocksdb,siddhartharay007/rocksdb,lgscofield/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,skunkwerks/rocksdb,tizzybec/rocksdb,lgscofield/rocksdb,wenduo/rocksdb,tsheasha/rocksdb,dkorolev/rocksdb,msb-at-yahoo/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,facebook/rocksdb,SunguckLee/RocksDB,mbarbon/rocksdb,temicai/rocksdb,msb-at-yahoo/rocksdb,lgscofield/rocksdb,alihalabyah/rocksdb,Andymic/rocksdb,JoeWoo/rocksdb,jalexanderqed/rocksdb,caijieming-baidu/rocksdb,tsheasha/rocksdb,tschottdorf/rocksdb,facebook/rocksdb,hobinyoon/rocksdb,alihalabyah/rocksdb,OverlordQ/rocksdb,amyvmiwei/rocksdb,sorphi/rocksdb,temicai/rocksdb,SunguckLee/RocksDB,Applied-Duality/rocksdb,luckywhu/rocksdb,Andymic/rocksdb,amyvmiwei/rocksdb,biddyweb/rocksdb,siddhartharay007/rocksdb,JackLian/rocksdb,virtdb/rocksdb,rDSN-Projects/rocksdb.replicated,OverlordQ/rocksdb,tsheasha/rocksdb,anagav/rocksdb,SunguckLee/RocksDB,makelivedotnet/rocksdb,anagav/rocksdb,tsheasha/rocksdb,luckywhu/rocksdb,vmx/rocksdb,rDSN-Projects/rocksdb.replicated,JoeWoo/rocksdb,mbarbon/rocksdb,lgscofield/rocksdb,wskplho/rocksdb,rDSN-Projects/rocksdb.replicated,wenduo/rocksdb,vmx/rocksdb,IMCG/RcoksDB,geraldoandradee/rocksdb,flabby/rocksdb,wenduo/rocksdb,wlqGit/rocksdb,temicai/rocksdb,amyvmiwei/rocksdb,zhangpng/rocksdb,NickCis/rocksdb,IMCG/RcoksDB,siddhartharay007/rocksdb,OverlordQ/rocksdb,IMCG/RcoksDB,wenduo/rocksdb,dkorolev/rocksdb,norton/rocksdb,Vaisman/rocksdb,sorphi/rocksdb,tizzybec/rocksdb,jalexanderqed/rocksdb,anagav/rocksdb,geraldoandradee/rocksdb,makelivedotnet/rocksdb,Applied-Duality/rocksdb,vashstorm/rocksdb,Vaisman/rocksdb,skunkwerks/rocksdb,siddhartharay007/rocksdb,kaschaeffer/rocksdb,Andymic/rocksdb,amyvmiwei/rocksdb,wskplho/rocksdb,ylong/rocksdb,biddyweb/rocksdb,wlqGit/rocksdb,dkorolev/rocksdb,JoeWoo/rocksdb,bbiao/rocksdb,caijieming-baidu/rocksdb,ryneli/rocksdb,Vaisman/rocksdb,wenduo/rocksdb,makelivedotnet/rocksdb,temicai/rocksdb,flabby/rocksdb,zhangpng/rocksdb,SunguckLee/RocksDB,ylong/rocksdb,JohnPJenkins/rocksdb,jalexanderqed/rocksdb,tschottdorf/rocksdb,bbiao/rocksdb,IMCG/RcoksDB,kaschaeffer/rocksdb,hobinyoon/rocksdb,kaschaeffer/rocksdb,lgscofield/rocksdb,geraldoandradee/rocksdb,tizzybec/rocksdb,makelivedotnet/rocksdb,ylong/rocksdb,sorphi/rocksdb,skunkwerks/rocksdb,NickCis/rocksdb,biddyweb/rocksdb,RyanTech/rocksdb,wat-ze-hex/rocksdb,temicai/rocksdb,norton/rocksdb,JohnPJenkins/rocksdb,alihalabyah/rocksdb,tizzybec/rocksdb,rDSN-Projects/rocksdb.replicated,zhangpng/rocksdb,ryneli/rocksdb,wskplho/rocksdb,SunguckLee/RocksDB,wlqGit/rocksdb,RyanTech/rocksdb,anagav/rocksdb,makelivedotnet/rocksdb,vashstorm/rocksdb,luckywhu/rocksdb,mbarbon/rocksdb,vashstorm/rocksdb,tschottdorf/rocksdb,JackLian/rocksdb,JohnPJenkins/rocksdb,jalexanderqed/rocksdb,mbarbon/rocksdb,wat-ze-hex/rocksdb,RyanTech/rocksdb,IMCG/RcoksDB,dkorolev/rocksdb,fengshao0907/rocksdb,bbiao/rocksdb,Andymic/rocksdb,anagav/rocksdb,OverlordQ/rocksdb,RyanTech/rocksdb,facebook/rocksdb,norton/rocksdb,Andymic/rocksdb,kaschaeffer/rocksdb,wlqGit/rocksdb,JohnPJenkins/rocksdb,sorphi/rocksdb,temicai/rocksdb,Applied-Duality/rocksdb,dkorolev/rocksdb,facebook/rocksdb,virtdb/rocksdb