Fix issue where InCallTonePlayer could fail to stop ringback.

The issue was that the code for stop tone was checking the mState.
Realistically that's what the latch was supposed to be for, so we don't
need to check the state.

Test: Manual test; reproduced using test app; verified that applied fix removed concurrency issue.
Fixes: 229765709
Change-Id: Ie8406c2a7010bbc48b9b269b1b6d266a08d9ab8a