Don't mirror ov7670 images by default.

The ov7670 sensor driver sets the mirror bit by default, which is not
the desired mode.  OLPC has been running with this patch for a while.
Signed-off-by: NJonathan Corbet <corbet@lwn.net>
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>