media: pxa-camera: Use v4l2_async_notifier_add_*_subdev

The use of v4l2_async_notifier_add_subdev will be discouraged.
Drivers are instead encouraged to use a helper such as
v4l2_async_notifier_add_fwnode_remote_subdev.

This fixes a misuse of the API, as v4l2_async_notifier_add_subdev
should get a kmalloc'ed struct v4l2_async_subdev.

Use the appropriate helper: v4l2_async_notifier_add_i2c_subdev
or v4l2_async_notifier_add_fwnode_remote_subdev, which handles
the needed setup, instead of open-coding it.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>