media: v4l: async: Move async subdev notifier operations to a separate structure

media: v4l: async: Move async subdev notifier operations to a separate structure

The async subdev notifier .bound(), .unbind() and .complete() operations
are function pointers stored directly in the v4l2_async_subdev
structure. As the structure isn't immutable, this creates a potential
security risk as the function pointers are mutable.

To fix this, move the function pointers to a new
v4l2_async_subdev_operations structure that can be made const in
drivers.

Signed-off-by: Laurent Pinchart <[email protected]>
Acked-by: Hans Verkuil <[email protected]>
Acked-by: Niklas Söderlund <[email protected]>
Reviewed-by: Sebastian Reichel <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>