ALSA: opti-miro: remove snd_card pointer from snd_miro structure

Remove the snd_card pointer from the snd_miro structure and
do some small code improvements.

Also, move Opti chipset detection before detection of the
ACI mixer, so the mci_base value is set in one place only.

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