media: ov2680: fix null dereference at power on

Swapping the order between v4l2 subdevice registration and checking chip
id in b7a41762 ("media: ov2680: don't register the v4l2 subdevice
before checking chip ID") makes the mode restore to use the sensor
controls before they are set, so move the mode restore call to s_power
after the handler setup for controls is done.

This remove also the need for the error code path in power on function.

Fixes: b7a41762 ("media: ov2680: don't register the v4l2 subdevice before checking chip ID")

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>