Provide a way to get the channel again

agb/src/sound/mixer/sw_mixer.rs

@@ -62,6 +62,16 @@ impl Mixer {
 
         panic!("Cannot play more than 16 sounds at once");
     }
+
+    pub fn get_channel(&mut self, id: ChannelId) -> Option<&'_ mut SoundChannel> {
+        if let Some(channel) = &mut self.channels[id.0] {
+            if self.indices[id.0] == id.1 {
+                return Some(channel);
+            }
+        }
+
+        None
+    }
 }
 
 // I've picked one frequency that works nicely. But there are others that work nicely