[media] ov9640: fix OmniVision OV9640 sensor driver's priv data retrieving

OmniVision OV9640 driver wasn't requesting properly its private data
on I2C remove and video_probe functions. It was retrieving the V4L2
subdev struct address instead of priv struct's one. This patch fixes
such problem.

Signed-off-by: David Cohen <dacohen@gmail.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>