ocarina: Change volume when volume slider changed

I pass along the new value to libsaria to set in the gstreamer pipeline.

gui/buttons/volume.cpp

@@ -1,4 +1,5 @@
 
+#include <libsaria/libsaria.h>
 #include <libsaria/print.h>
 #include <ocarina/button.h>
 
@@ -24,6 +25,7 @@ static void set_increment(GtkWidget *volume, double incr)
 
 static void changed(GtkWidget *button, gdouble value, gpointer data)
 {
+	libsaria_get()->set_volume(value);
 	resize(button);
 }