The release of the dma channels was being performed in prepare and there was a
edma_resume call for the asp-channel only being executed on START, RESUME and
PAUSE_RELEASE.

The mcasp on da850evm with ping-pong buffers enabled was exhibiting an audible
glitch on every playback after the first. It was determined through trial and
error that the following two changes fix this problem:

1) Move the edma_start calls from prepare to trigger and 2) reverse the order
of starting the asp and ram channels.
Signed-off-by: NBen Gardiner <bengardiner@nanometrics.ca>
Reviewed-by: NSteven Faludi <stevenfaludi@nanometrics.ca>
Acked-by: NLiam Girdwood <lrg@ti.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>