ALSA: dice: Rename structure and its members

Currently, dice driver supports AMDTP out-stream. In followed commits, AMDTP
in-stream will be supported but current name of members in dice structure
are not propper. This commit renames these members to proper name.

Additionally, for easily distinguishing local symbols from structure tag,
rename dice tag into snd_dice.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>