media: i2c: imx290: Initialize runtime PM before subdev

Initializing the subdev before runtime PM means that no subdev
initialization can interact with the runtime PM framework. This can be
problematic when modifying controls, as the .s_ctrl() handler commonly
calls pm_runtime_get_if_in_use(). These code paths are not trivial,
making the driver fragile and possibly causing subtle bugs.

To make the subdev initialization more robust, initialize runtime PM
first.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-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>