service/pipewire: set device node volumes with device object

Fixes discrepancies between pulse and qs volumes, and volumes not
persisting across reboot or vt switches.

src/services/pipewire/node.hpp

@@ -18,6 +18,8 @@
 
 namespace qs::service::pipewire {
 
+class PwDevice;
+
 ///! Audio channel of a pipewire node.
 /// See @@PwNodeAudio.channels.
 class PwAudioChannel: public QObject {
@@ -161,6 +163,9 @@ public:
 
 	PwNodeBoundData* boundData = nullptr;
 
+	PwDevice* device = nullptr;
+	qint32 routeDevice = -1;
+
 signals:
 	void propertiesChanged();