Incorrect _COMMTIMEOUTS struct in serial_windows.go

The correct field order should be like this:

``` go
type _COMMTIMEOUTS struct {
    ReadIntervalTimeout         uint32
    ReadTotalTimeoutConstant    uint32
    ReadTotalTimeoutMultiplier  uint32
    WriteTotalTimeoutConstant   uint32
    WriteTotalTimeoutMultiplier uint32
}
```

See comments there: http://msdn.microsoft.com/en-us/library/windows/desktop/aa363190%28v=vs.85%29.aspx
