Add missing my_pid to fprintf in multi_process_example (#6731)

Summary:
Signed-off-by: Derrick Pallas <derrick@pallas.us>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6731

Reviewed By: siying

Differential Revision: D21137005

Pulled By: riversand963

fbshipit-source-id: a7182e1bec225bc110971f40e2d0e6c3a671c061

examples/multi_processes_example.cc

@@ -301,7 +301,7 @@ void RunSecondary() {
       std::string value;
       db->Get(ropts, key, &value);
     }
-    fprintf(stdout, "[process %ld] Point lookup thread finished\n");
+    fprintf(stdout, "[process %ld] Point lookup thread finished\n", my_pid);
   });
 
   uint64_t curr_key = 0;