perf maps: Use maps__nr_maps() instead of open coded maps->nr_maps

To use the existing accessor and be consistent.
Signef-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/machine.c

@@ -435,7 +435,7 @@ static struct thread *findnew_guest_code(struct machine *machine,
 		return NULL;
 
 	/* Assume maps are set up if there are any */
-	if (thread->maps->nr_maps)
+	if (maps__nr_maps(thread->maps))
 		return thread;
 
 	host_thread = machine__find_thread(host_machine, -1, pid);