V4L/DVB (10666): ov772x: move configuration from start_capture() to set_fmt()

soc_camera framework requires, that camera configuration is performed in
set_fmt, and start_capture and stop_capture only turn the camera on/off.
This patch modifies ov772x to comply to this requirement.

Signed-off-by: Kuninori Morimoto <morimoto.kuninori@renesas.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>