kitakami-common: Restore audio tuning mixer control

 * After all, this still seems to be needed for ACDB MCS init,
   as seen bellow. Just let ACDB loader be happy.

   Without the tuning mixer file:
     E ACDB-MCS: acdb_mcs_init: /vendor/etc/audio_tuning_mixer_tasha.txt not present, using /vendor/etc/audio_tuning_mixer.txt config file
     E MCS-RT-CTL: Can't open the configuration file /vendor/etc/audio_tuning_mixer.txt.
     E ACDB-MCS: acdb_mcs_init: MCS routing control initialization failed.

   With the tuning mixer file:
     E ACDB-MCS: acdb_mcs_init: /vendor/etc/audio_tuning_mixer_tasha.txt not present, using /vendor/etc/audio_tuning_mixer.txt config file
     D         : [ACPH]->MCS RTC service registered with ACPH

Change-Id: I6e4b1fe27547a354eaa4132aba8e3df04d6184b3