Fix a compilation error in ROCKSDB_LITE in db/internal_stats.h
Fix a compilation error in ROCKSDB_LITE in db/internal_stats.h

Summary:
Fix a compilation error in ROCKSDB_LITE in db/internal_stats.h

Other compilation errors will be fixed in a separate diff.

Test Plan: make OPT=-DROCKSDB_LITE

Reviewers: sdong, igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D36807

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