ALSA: ctl: bump protocol version up to v2.1.0

ALSA: ctl: bump protocol version up to v2.1.0

In a development period for v5.6 kernel, some changes are introduced to
structures in ALSA control interface:
 - 'tstamp' member is removed from 'struct snd_ctl_elem_value
 - 'TSTAMP' flag is removed from a set of access flags for 'struct
   snd_ctl_elem_info'
 - 'dimen' member is removed from 'struct snd_ctl_elem_info

Although these changes were introduced with enough consideration for
backward compatibility, they include slightly lose of it. This commit
bumps protocol version of ALSA control interface up to v2.1.0.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191223023921.8151-5-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>