Bluetooth: Controller: Fix leak in Num Completed Packets

Fix a leak in generation of Number of Completed Packets when
more than one handle has acknowledgements to be processed.

The loop exited for the current handle by dequeueing the
node tx element of the next handle leading to lost Number of
Completed Packets.

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