Fix compile warning in db/db_impl

Summary:
Fix the following compile warning in db/db_impl

  db/db_impl.cc:1603:19: error: implicit conversion loses integer precision: 'const uint64_t' (aka 'const unsigned long') to 'int' [-Werror,-Wshorten-64-to-32]
     info.job_id = job_id;
                 ~ ^~~~~~

Test Plan: db_test

Reviewers: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D39423

db/db_impl.cc

@@ -1584,7 +1584,7 @@ Status DBImpl::CompactFilesImpl(
 void DBImpl::NotifyOnCompactionCompleted(
     ColumnFamilyData* cfd, Compaction *c, const Status &st,
     const CompactionJobStats& compaction_job_stats,
-    const uint64_t job_id) {
+    const int job_id) {
 #ifndef ROCKSDB_LITE
   if (db_options_.listeners.size() == 0U) {
     return;

db/db_impl.h

@@ -353,7 +353,7 @@ class DBImpl : public DB {
   void NotifyOnCompactionCompleted(ColumnFamilyData* cfd,
                                    Compaction *c, const Status &st,
                                    const CompactionJobStats& job_stats,
-                                   uint64_t job_id);
+                                   int job_id);
 
   void NewThreadStatusCfInfo(ColumnFamilyData* cfd) const;