configs: msmnile: update gain control for headset-mic

Headset mic was updated to use DEC1 instead of DEC0,
Update gain control accordingly to reduce its level
and have it set to appropriate level.
This is required to pass CTS verifier LoopBack Latency
test case on wired headset loopback dongle.

Change-Id: I8d0f3f673b8306458a0d9ed151374c5b54121e07