AudioFocusTest: fix flakiness on focus freeze

Failing to freeze focus for non-test UIDs shouldn't be considered
a test failure due to the potential of overlapping runs. Only
log a message when enterAudioFocusFreezeForTest fails.

Bug: 335135679
Test: atest android.media.audio.cts.AudioFocusTest
Change-Id: I83b9963fc8ed5e0e1403afef43fdc8fab0d31d56