chore(apu): change access modifiers of some methods

src/cpu.rs

@@ -1,4 +1,4 @@
-use crate::apu::gen::AudioSender;
+use crate::apu::Apu;
 use crate::bus::{Bus, BusIo};
 use crate::instruction::{Cycle, Instruction};
 use crate::interrupt::{InterruptEnable, InterruptFlag};
@@ -45,10 +45,6 @@ impl Cpu {
         })
     }
 
-    pub fn set_audio_src(&mut self, sender: AudioSender<f32>) {
-        self.bus.pass_audio_src(sender)
-    }
-
     pub(crate) fn ime(&self) -> ImeState {
         self.ime
     }
@@ -174,6 +170,10 @@ impl Cpu {
         &self.bus.ppu
     }
 
+    pub fn apu_mut(&mut self) -> &mut Apu {
+        &mut self.bus.apu
+    }
+
     pub(crate) fn joypad_mut(&mut self) -> &mut Joypad {
         &mut self.bus.joypad
     }