Bluetooth: Controller: Fix scheduling of Periodic Advertising events

Fix scheduling of Periodic Advertising events to be after
the group of Auxiliary set events. Do not reduce the slot
offsets as time reservations in ticker for non low latency
variant of controller does not include the slot offsets in
the reservation.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>