audio_core/cubeb_sink: Resolve variable shadowing warnings in SamplesInQueue

The name of the parameter was shadowing the member variable of the same
name. Instead, alter the name of the parameter to prevent said
shadowing.

src/audio_core/cubeb_sink.cpp

@@ -75,11 +75,11 @@ public:
         queue.Push(samples);
     }
 
-    std::size_t SamplesInQueue(u32 num_channels) const override {
+    std::size_t SamplesInQueue(u32 channel_count) const override {
         if (!ctx)
             return 0;
 
-        return queue.Size() / num_channels;
+        return queue.Size() / channel_count;
     }
 
     void Flush() override {