leaudio: Fix for bad audio when one earbud connected

Fix is configuring Audio Session for 2 channels always, as other part of
code expect this.

Bug: 212490645
Bug: 150670922
Test: Manual test audio on single earbud.
Sponsor: @jpawlowski
Change-Id: I6863faab53bd025daa1d0df07140a64504a60df4