This is a follow up on 53dea36c70 which fixes the other affected
pcm engines.
Description from 53dea36c70c1857:
Don't rely on the codec's channels_min information to decide wheter or
not allocate a substream's DMA buffer. Rather check if the substream
itself was allocated previously.
Without this patch I was seeing null-pointer dereferenc in atmel-pcm.
Signed-off-by: Joachim Eastwood <joachim.eastwood@jotron.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>