[media] ov772x: Select the default format at probe time

The format and window size are only initialized during the first g_fmt
call. This leaves the device in an inconsistent state after
initialization, which will cause problems when implementing pad
operations. Move the format and window size initialization to probe
time.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>