Cleanup build warnings for Audio HAL

The code for Audio HAL causes a set of build warnings related to
such things as unused variables, constant cast-aways and others

This commit cleans up all warnings yielding a clean build of
the HAL codebase

Bug: None
Test: build
Change-Id: Ie0c2de6d2c4b2f900d021be4e04ef6e9ce13140f
1 file changed