media: i2c: imx334: Enable runtime PM before sub-device registration

Runtime PM is fully initialized before calling
v4l2_async_register_subdev_sensor(). Moving the runtime PM initialization
earlier prevents potential access to an uninitialized or powered-down
device.

Signed-off-by: Tarang Raval <tarang.raval@siliconsignals.io>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>