ASoC: dwc: Iterate over all channels

The Designware core can be configured with up to four stereo channels.
Each stereo channel is individually configured so, when the driver's
hw_params call is made, each requested stereo channel has to be
programmed.

Signed-off-by: Andrew Jackson <Andrew.Jackson@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>