Reduce video frame drop rate

The video playback engine depends on having relatively precise audio
progress updates for its A/V sync and frame drop calculations.  For small
audio HAL buffer sizes, this was not a problem, but when the HAL buffer
size was > 12 ms, the normal mix buffer size became > 24 ms and this
then caused video problems.  The new formula tries to keep the normal
mix buffer size within a closer tolerance of 20 ms to 24 ms.

Also use consistent term: multiplier instead of multiple.

Bug: 6479613
Change-Id: I903bad74461908e8c8f0a61e99ab5e24d5c44433