[media] ov7670: use colorspace SRGB instead of JPEG

Even though the format is Y'CbCr, the colorspace used by the sensor
is almost certainly SRGB. The sensor is also not generating JPEG data,
so it makes no sense to use V4L2_COLORSPACE_JPEG here.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>