ASoC: SOF: ipc3-topology: Set scontrol->priv to NULL after freeing it

Since the scontrol->priv is freed up during load operation it should be set
to NULL to be safe against double freeing attempt.

Fixes: b5cee8fe ("ASoC: SOF: topology: Make control parsing IPC agnostic")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20220331114757.32551-1-peter.ujfalusi@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>