Bluetooth: Controller: Fix uninitialized pointer read of SR ADI

When Extended Scan Response data of length zero is set, the
Scan Response do not have the Common Extended Payload Format
and hence no ADI field. Fix uninitialized pointer to Scan
Response Data's ADI to avoid copy of ADI from primary
channel PDU.

Fixes #38015.

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