Set default window and format code at probe time instead of always checking
if they have not been set yet when VIDIOC_SUBDEV_G_FMT ioctl is called.

This change simplifies the next patch (make VIDIOC_SUBDEV_G_FMT ioctl work
with V4L2_SUBDEV_FORMAT_TRY).
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>