[media] go7007: fix i2c_xfer return codes

The i2c_xfer functions didn't return the proper error codes and (especially
important) on success they returned 0 instead of the number of transferred
messages.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>