Mcp23017 initialization resets pin values

**Describe the bug**

Every time a new instance of Mcp23017() is being created the pins are being reset to low. This is an issue when the written software reboots, eg when updating the software version.

**Steps to reproduce**

```csharp
var pinNumber = 0;

var i2cConnectionSettings = new I2cConnectionSettings(1, 0x20);

var i2cDevice = I2cDevice.Create(i2cConnectionSettings);

var device = new Mcp23017(i2cDevice);

var controller = new GpioController(PinNumberingScheme.Logical, Mcp23017Device);

controller.Write(pinNumber, PinValue.High);

var device2 = new Mcp23017(i2cDevice);

var pinValue = controller.Read(pinNumber);
```

**Expected behavior**

Pins need to keep their value after re-initializing the Mcp23017() adapter.

**Actual behavior**

Pins are being reset every time a new instance of Mcp23017() is being declared. Looks like it is embedded in the init code here:
https://github.com/dotnet/iot/blob/main/src/devices/Mcp23xxx/Mcp23xxx.cs - starting at line 84.

从 src/devices/Mcp23xxx/Mcp23xxx.cs 第 84 行附近开始，这里执行了 Mcp23017 的初始化。复现创建适配器、将一个引脚写为 high 以及创建第二个适配器的顺序；当引脚在重新初始化后仍保留其值时即完成。

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