Use the V4L2 subdev active state API to store the active format. This
simplifies the driver not only by dropping the imx290 current_format
field, but it also allows dropping the imx290 lock, replaced with the
state lock.

The lock check in imx290_ctrl_update() can be dropped as
imx290_set_fmt() can't be called anywmore with which set to ACTIVE
before controls are initialized.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>