downmix: Fix aliasing violation

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
av: Fix compile errors

Don't use memcpy() on areas that may overlap
Fix aliasing violation

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
fix typo in a previous commit

Change-Id: I226ea02d844e2daba4080f1902694d1511664690
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
build error should be fixed too