Bug Neopixel on WROOM ESP32

Bug Neopixel on WROOM ESP32

I used this ocde
```
np = machine.Neopixel(machine.Pin(13), 128, machine.Neopixel.TYPE_RGB)
np.set(51, machine.Neopixel.GREEN)
np.show()
```

And a get this error after 3 times of execution

```
>>> %Run -c $EDITOR_CONTENT
Traceback (most recent call last):
  File "<stdin>", line 12, in <module>
ValueError: Cannot acquire RMT channel
```