io/i2c: depend on ioctl calls to read/write

Tested with a Grove-LCD RGB Backlight.

Updates golang/go#15264.

Change-Id: Iba3653de83c2355686674907ee93bed0cb17a663
Reviewed-on: https://go-review.googlesource.com/21960
Reviewed-by: Minux Ma <minux@golang.org>
3 files changed