Fix DisconnectedCallNotifierTest

Some recent change deep in the bowels of the notification code was
causing a NPE because it was accessing something we weren't mocking.
This changes adds the correct mocking line to fix this issue.

Fixes: 175217162
Test: atest DisconnectedCallNotifierTest
Change-Id: Ia1cdccb44f6258d60e11481aea0794b1cc3a3b5e
1 file changed