Update notification iterator's "init" function signature

Update notification iterator's "init" function signature

As per this project's standard way of calling methods, the self object
should always be the first parameter. In the cast of
bt_component_class_notification_iterator_init_method, we don't need to
explicitly pass the bt_private_component object since you can get it
from the notification iterator with
bt_private_notification_iterator_get_private_component().

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>