ASoC: SOF: enable dual control for pga

Currently sof pga element supports only 1 kcontrol and you can't create
for example a mixer element with combined volume slider and mute switch.
So enable sof pga to have more than 1 kcontrol associated with it. Also
check for possible NULL tlv pointer as switch element might not have it.
Signed-off-by: Jaska Uimonen <jaska.uimonen@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191008164443.1358-8-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/topology.c

@@ -1580,7 +1580,7 @@ static int sof_widget_load_pga(struct snd_soc_component *scomp, int index,
 	if (!volume)
 		return -ENOMEM;
 
-	if (le32_to_cpu(tw->num_kcontrols) != 1) {
+	if (!le32_to_cpu(tw->num_kcontrols)) {
 		dev_err(sdev->dev, "error: invalid kcontrol count %d for volume\n",
 			tw->num_kcontrols);
 		ret = -EINVAL;
@@ -1617,7 +1617,8 @@ static int sof_widget_load_pga(struct snd_soc_component *scomp, int index,
 	swidget->private = volume;
 
 	list_for_each_entry(scontrol, &sdev->kcontrol_list, list) {
-		if (scontrol->comp_id == swidget->comp_id) {
+		if (scontrol->comp_id == swidget->comp_id &&
+		    scontrol->volume_table) {
 			min_step = scontrol->min_volume_step;
 			max_step = scontrol->max_volume_step;
 			volume->min_value = scontrol->volume_table[min_step];