ASoC: SOF: sof-audio: skip prepare/unprepare if swidget is NULL

Skip preparing/unpreparing widgets if the swidget pointer is NULL. This
will be true in the case of virtual widgets in topology that were added
for reusing the legacy HDA machine driver with SOF.

Fixes: 9862dcf7 ("ASoC: SOF: don't unprepare widget used other pipelines")
Cc: <stable@vger.kernel.org> # 6.1
Signed-off-by: NRanjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: NRander Wang <rander.wang@intel.com>
Reviewed-by: NAngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: NAngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/20230118101255.29139-3-peter.ujfalusi@linux.intel.comSigned-off-by: NMark Brown <broonie@kernel.org>

sound/soc/sof/sof-audio.c

@@ -272,7 +272,7 @@ sof_unprepare_widgets_in_path(struct snd_sof_dev *sdev, struct snd_soc_dapm_widg
 	struct snd_soc_dapm_path *p;
 
 	/* return if the widget is in use or if it is already unprepared */
-	if (!swidget->prepared || swidget->use_count > 0)
+	if (!swidget || !swidget->prepared || swidget->use_count > 0)
 		return;
 
 	if (widget_ops[widget->id].ipc_unprepare)
@@ -303,7 +303,7 @@ sof_prepare_widgets_in_path(struct snd_sof_dev *sdev, struct snd_soc_dapm_widget
 	struct snd_soc_dapm_path *p;
 	int ret;
 
-	if (!widget_ops[widget->id].ipc_prepare || swidget->prepared)
+	if (!swidget || !widget_ops[widget->id].ipc_prepare || swidget->prepared)
 		goto sink_prepare;
 
 	/* prepare the source widget */