ASoC: wm_adsp: Show avail in bytes to match other messages

All other debug messages talk about data on the compressed stream in
bytes except avail which is shown in words. To avoid confusion show
avail in bytes as well.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>