media: rkisp1: Use fwnode_graph_for_each_endpoint

When registering the notifier, replace the manual while loop with
fwnode_graph_for_each_endpoint. This simplifies error handling.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Dafna Hirschfeld <dafna@fastmail.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>