Report correct name in autovacuum "work items" activity

We were reporting the database name instead of the relation name to
pg_stat_activity.  Repair.

Reported-by: Justin Pryzby
Discussion: https://postgr.es/m/20190220185552.GR28750@telsasoft.com

src/backend/postmaster/autovacuum.c

@@ -2633,7 +2633,7 @@ perform_work_item(AutoVacuumWorkItem *workitem)
 	if (!cur_relname || !cur_nspname || !cur_datname)
 		goto deleted2;
 
-	autovac_report_workitem(workitem, cur_nspname, cur_datname);
+	autovac_report_workitem(workitem, cur_nspname, cur_relname);
 
 	/* clean up memory before each work item */
 	MemoryContextResetAndDeleteChildren(PortalContext);