[ALSA] dynamic minors (2/6): simplify storage of snd_minor structures

Modules: ALSA Core

Store the snd_minor structure pointers in one array instead of using a
separate list for each card.  This simplifies the mapping from device
files to minor struct by removing the need to know about the encoding
of the card number in the minor number.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>