[ALSA] ca0106: remove extra commands in SPI DAC init sequence

The init sequence set a number of registers more than once to different
values.  It's only necessary to set them once to their final values.
It also never actually updated the digital attenuation settings.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>