ASoC: If we can't find a cache compression type default to flat

This makes it easier to make cache types build time configurable as we
don't have a hard dependency on a given cache being built in.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>

diff --cc sound/soc/soc-cache.c
Simple merge