Telecomm: Fix PhoneAccountRegistrarTest

Fix state comparison in PhoneAccountRegistrarTest to actually do
something (and not compare nulls).

Found by Errorprone.

(cherry picked from commit fb7a391b)

Bug: 73288226
Test: m javac-check RUN_ERROR_PRONE=true
Test: atest PhoneAccountRegistrarTest
Merged-In: Ied3b3b3e38e3b73a37479dd2bdbac8a3e3fc3228
Change-Id: Ied3b3b3e38e3b73a37479dd2bdbac8a3e3fc3228