Now that all Extensible classes expose a _d() function that performs
appropriate casts, the LIBCAMERA_D_PTR brings no real additional value.
Replace it with direct calls to the _d() function.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>