hda-codec: fix playback rate control

hda-codec: fix playback rate control

Since commit 1930616b98 "audio: make mixeng optional" the
function hda_audio_output_cb can no longer assume the function
parameter avail contains the free buffer size. With the playback
mixing-engine turned off this leads to a broken playback rate
control and playback buffer drops in regular intervals.

This patch moves down the rate calculation, so the correct
buffer fill level is used for the calculation.

Signed-off-by: Volker Rümelin <[email protected]>
Message-id: 20200104091122[email protected]
Signed-off-by: Gerd Hoffmann <[email protected]>