ASoC: atmel-pcm-dma: won't check direction when configure dma

As DMA framework request DMA using direction only in prep_slave
function, (The At91 xdma driver has adapted to this request).
So won't check direction when do DMA configuration.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>