Revert "hal: set backend channel number to one for mono speaker"

This reverts commit bd55e0be3b4a2747e96ee240ec794f1c432fdbea.
Removal of HAL access to channel mixer ctrl fixes the issue
as a better approach.

Change-Id: I5457bbc2e5185047289f440cbea222a6592f71b1
1 file changed