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