[ALSA] soc - fix s3c2410 PCM breakage

S3C2410 pcm doesn't work.
s3c2410_dma_request() now returns the channel number and not 0 if OK.

Signed-off-by: Davide Rizzo <davide@elpa.it>
Acked-by: Liam Girdwood <lg@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>