media: ov2640: make VIDIOC_SUBDEV_G_FMT ioctl work with V4L2_SUBDEV_FORMAT_TRY

The VIDIOC_SUBDEV_G_FMT ioctl for this driver doesn't recognize
V4L2_SUBDEV_FORMAT_TRY and always works as if V4L2_SUBDEV_FORMAT_ACTIVE
is specified.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>