Fixing the documentation of the function (#4803)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6354

Differential Revision: D19725459

Pulled By: riversand963

fbshipit-source-id: fded24576251bfa4b289399f0909f1fe43426e28

include/rocksdb/db.h

@@ -1410,9 +1410,9 @@ class DB {
 
 #endif  // ROCKSDB_LITE
 
-  // Sets the globally unique ID created at database creation time by invoking
+  // Returns the unique ID which is read from IDENTITY file during the opening
-  // Env::GenerateUniqueId(), in identity. Returns Status::OK if identity could
+  // of database by setting in the identity variable
-  // be set properly
+  // Returns Status::OK if identity could be set properly
   virtual Status GetDbIdentity(std::string& identity) const = 0;
 
   // Returns default column family handle