Bluetooth: Controller: Fix Periodic Sync LLL scheduling flag

Fix Periodic Advertising Sync LLL scheduling flag to not be
set when chain PDUs use LLL scheduling, only set when
primary AUX_SYNC_IND PDU received use LLL scheduling.

Without the fix, spurious EVENT_DONE_EXTRA_TYPE_SYNC would
be generated when chain PDUs are failed to be received. This
can cause Sync Lost message to be generated.

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