monitor: fix debug print compiling error

error: 'i' undeclared (first use in this function)
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

monitor.c

@@ -4747,8 +4747,11 @@ static void monitor_find_completion(void *opaque,
         return;
     }
 #ifdef DEBUG_COMPLETION
-    for (i = 0; i < nb_args; i++) {
-        monitor_printf(mon, "arg%d = '%s'\n", i, args[i]);
+    {
+        int i;
+        for (i = 0; i < nb_args; i++) {
+            monitor_printf(mon, "arg%d = '%s'\n", i, args[i]);
+        }
     }
 #endif