WriteRegU16LE typo

Please fix typo

Now in https://github.com/d2r2/go-i2c/blob/master/i2c.go#L209 was `*` instead of `&`
```go
w := (value*0xFF00)>>8 + value<<8
```

Fixed line:
```go
w := (value&0xFF00)>>8 + value<<8
```

But this variant more correct:
```go
w := (value>>8)|(value<<8)
```