ALSA: ctl: remove dimen member from elem_info structure

ALSA: ctl: remove dimen member from elem_info structure

The 'dimen' member of 'struct snd_ctl_elem_info' is designed to deliver
information to use an array of value as multi-dimensional values. This
feature is used just by echoaudio PCI driver, and fortunately it's not
used by the other applications than 'echomixer' in alsa-tools.

In a previous commit, usage of 'dimen' member is removed from echoaudio
PCI driver. Nowadays no driver/application use the feature.

This commit removes the member from structure.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191223023921.8151-4-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>