Fix Valgrind error introduced by D16515

Summary: valgrind reports issues. This patch seems to fix it.

Test Plan: run the tests that fails in valgrind

Reviewers: igor, haobo, kailiu

Reviewed By: kailiu

CC: dhruba, ljin, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D16653

include/rocksdb/env.h

@@ -584,7 +584,7 @@ class LogBuffer {
   ~LogBuffer();
 
   // Add a log entry to the buffer.
-  void AddLogToBuffer(const char* format, ...);
+  void AddLogToBuffer(const char* format, va_list ap);
 
   // Flush all buffered log to the info log.
   void FlushBufferToLog() const;