将V8中的deviceIp字段设为只读，解决IDE0044警告

Windows/CS/Framework4.0/Toprie/Toprie/V8.cs

@@ -128,7 +128,7 @@ namespace JoyD.Windows.CS.Toprie
         }
 
         // 私有字段
-        private string deviceIp;
+        private readonly string deviceIp;
         private Socket socket = null;
         private static bool isSdkInitialized = false;
         private static readonly Dictionary<string, V8> deviceInstances = new Dictionary<string, V8>();