misc: chore: Use explicit types in audio projects

src/Ryujinx.Audio.Backends.SDL2/SDL2HardwareDeviceDriver.cs

@@ -37,7 +37,7 @@ namespace Ryujinx.Audio.Backends.SDL2
 
             SDL2Driver.Instance.Initialize();
 
-            int res = SDL_GetDefaultAudioInfo(nint.Zero, out var spec, 0);
+            int res = SDL_GetDefaultAudioInfo(nint.Zero, out SDL_AudioSpec spec, 0);
 
             if (res != 0)
             {

src/Ryujinx.Audio.Backends.SoundIo/Native/SoundIoOutStreamContext.cs

@@ -38,7 +38,7 @@ namespace Ryujinx.Audio.Backends.SoundIo.Native
             get => Marshal.PtrToStringAnsi(GetOutContext().Name);
             set
             {
-                var context = GetOutContext();
+                SoundIoOutStream context = GetOutContext();
 
                 if (_nameStored != nint.Zero && context.Name == _nameStored)
                 {
@@ -129,8 +129,8 @@ namespace Ryujinx.Audio.Backends.SoundIo.Native
 
             unsafe
             {
-                var frameCountPtr = &nativeFrameCount;
-                var arenasPtr = &arenas;
+                int* frameCountPtr = &nativeFrameCount;
+                IntPtr* arenasPtr = &arenas;
                 CheckError(soundio_outstream_begin_write(_context, (nint)arenasPtr, (nint)frameCountPtr));
 
                 frameCount = *frameCountPtr;

src/Ryujinx.Audio/Renderer/Utils/FileHardwareDevice.cs

@@ -27,7 +27,7 @@ namespace Ryujinx.Audio.Renderer.Utils
 
         private void UpdateHeader()
         {
-            var writer = new BinaryWriter(_stream);
+            BinaryWriter writer = new(_stream);
 
             long currentPos = writer.Seek(0, SeekOrigin.Current);