Fix default control source name in PPA release script

Summary:
D8295 missed setting a default CONTROL_SOURCE_NAME, so not
setting --network will always fail.

Test Plan:

./debian-packages.sh -p jasonbcox-bitcoin-abc jasonbcox

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8338