Bluetooth: Controller: Fix Periodic Sync for multiple chain reception

Fix regression introduced in Periodic Advertising
Synchronization due to change related to multiple
Advertising chain reception.

Related commit c334ed51 ("Bluetooth: Controller: Fix
multiple Extended Adv chain reception"), and
commit da792a9e ("Bluetooth: Controller: Fix interleaved
extended scanning assert").

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