Remove KSAUDIO_SPEAKER_2POINT1 because it is included in the Windows
SDK. (I'm guessing it wasn't before.)
Redefine 4POINT1 as KSAUDIO_SPEAKER_SURROUND|SPEAKER_LOW_FREQUENCY
instead of KSAUDIO_SPEAKER_QUAD|SPEAKER_LOW_FREQUENCY. See definitions:
FFmpeg 4.1: FL+FR+FC+LFE+BC
WASAPI QUAD: FL+FR+BL+BR (looks wrong)
WASAPI SURROUND: FL+FR+FC+BC
WASAPI LOW_FREQUENCY: LFE