io/i2c: make sure len(r) number of bytes are read

ReadFull ensures that err = nil, iff len(r) number of bytes are read.

Change-Id: I0453518646c5751f3b185d935b74763959a02ef8
Reviewed-on: https://go-review.googlesource.com/23603
Reviewed-by: Minux Ma <minux@golang.org>
1 file changed