audio: Headers said 5 channel is quad+center, but it's 4.1.

include/SDL_audio.h

@@ -172,7 +172,7 @@ typedef void (SDLCALL * SDL_AudioCallback) (void *userdata, Uint8 * stream,
  *  2:  FL FR                       (stereo)
  *  3:  FL FR LFE                   (2.1 surround)
  *  4:  FL FR BL BR                 (quad)
- *  5:  FL FR FC BL BR              (quad + center)
+ *  5:  FL FR LFE BL BR             (4.1 surround)
  *  6:  FL FR FC LFE SL SR          (5.1 surround - last two can also be BL BR)
  *  7:  FL FR FC LFE BC SL SR       (6.1 surround)
  *  8:  FL FR FC LFE BL BR SL SR    (7.1 surround)