ALSA: ca0106 MSI K8N Diamond MB spi_dac 2->1

This patch removes an inconsistency that became apparent when I
documented the fields of snd_ca0106_details. spi_dac is always
used in a 'boolean' sense, so this cleanup should make no difference.

[Actually, there is one place checking explicitly spi_dac == 1, so
 this will change the behavior.  But, supposing it's rather a typo,
 I apply this clean-up patch -- tiwai]

Signed-off-by: Ben Stanley <Ben.Stanley@exemail.com.au>
Signed-off-by: Takashi Iwai <tiwai@suse.de>