AudioServer: Use first audio channel in the /dev/audio directory

For now, just use the first audio channel in the /dev/audio directory.
In the future we can add support for watching and loading other channels
so we can route audio to multiple sound cards on the system.

Userland/Services/AudioServer/Mixer.cpp

@@ -23,7 +23,8 @@ namespace AudioServer {
 u8 Mixer::m_zero_filled_buffer[4096];
 
 Mixer::Mixer(NonnullRefPtr<Core::ConfigFile> config)
- : m_device(Core::File::construct("/dev/audio", this))
+ // FIXME: Allow AudioServer to use other audio channels as well
+ : m_device(Core::File::construct("/dev/audio/0", this))
  , m_sound_thread(Threading::Thread::construct(
  [this] {
  mix();