media: ov7670: don't return ENOTTY if SUBDEV_API is not set

If CONFIG_VIDEO_V4L2_SUBDEV_API is not set, then it is still possible
to call set_fmt for V4L2_SUBDEV_FORMAT_TRY, the result is just not
stored. So return 0 instead of -ENOTTY.

Calling get_fmt with V4L2_SUBDEV_FORMAT_TRY should return -EINVAL
instead of -ENOTTY, after all the get_fmt functionality is still
present, just not supported for TRY.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>