SDL: set the playback format with native endianness

This fixes sound playback on big-endian machines.

Fixes: #329

src/FAudio_platform_sdl2.c

@@ -149,7 +149,7 @@ void FAudio_PlatformInit(
 
  /* Build the device spec */
  want.freq = mixFormat->Format.nSamplesPerSec;
- want.format = AUDIO_F32;
+ want.format = AUDIO_F32SYS;
  want.channels = mixFormat->Format.nChannels;
  want.silence = 0;
  want.callback = FAudio_INTERNAL_MixCallback;