ASoC: SOF: sof-audio: Drop the `cmd` member from struct snd_sof_control

ASoC: SOF: sof-audio: Drop the `cmd` member from struct snd_sof_control

There is no need to use two variables to store and check the same
information, the scontrol->cmd is the same as scontrol->control_data->cmd.

Drop the former one and when it is needed, access the cmd from the
control_data.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20211215180404.53254-6-ranjani.sridharan@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>