V4L/DVB: ov7670: Don't use SMBUS I/O

Contrary to my earlier belief, the ov7670 is not actually an SMBUS device,
though it will pretend to be one if it's in a good mood.  Unfortunately,
it's rarely in a good mood, especially on the XO 1.5.  So use low-level i2c
I/O instead.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>