Fix a warning.

mini_al.h

@@ -8843,6 +8843,8 @@ mal_result mal_device_init__sdl(mal_context* pContext, mal_device_type type, mal
     mal_assert(pConfig != NULL);
     mal_assert(pDevice != NULL);
 
+    (void)pContext;
+
     // SDL wants the buffer size to be a power of 2. The SDL_AudioSpec property for this is only a Uint16, so we need
     // to explicitly clamp this because it will be easy to overflow.
     mal_uint32 bufferSize = pConfig->bufferSizeInFrames;