ALSA: es968: fix wrong PnP dma index

There is only one dma for the ESS ES968 based board.
Its index is 0 and not 1.

This make the es968 card working.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>