Kernel/Audio: Implement 2 correctness fixes in AC97

The fixes are:
1. Don't copy PCI::DeviceIdentifier during construction. This is a heavy
structure to copy so we definitely don't want to do that. Instead, use
a const reference to it like what happens in other parts in the Kernel.
2. Declare the constructor as explicit to avoid construction errors.

Kernel/Devices/Audio/AC97.h

@@ -145,7 +145,7 @@ private:
         StringView m_name;
     };
 
-    AC97(PCI::DeviceIdentifier);
+    explicit AC97(PCI::DeviceIdentifier const&);
 
     // ^IRQHandler
     virtual bool handle_irq(const RegisterState&) override;