DownmixProcess: Add a check to verify that input and output frame counts are same.

After downmix process the input and output frame size are different.
Modified the check to compare the frame counts.
Modified the channel mask validation check.

Bug:
Test: atest VtsHalDownmixTargetTest
Change-Id: Iad7014e2a1c929d748e8c8f90ee07ba13da7fe03
1 file changed