AESinkALSA: Fix S24NE4MSB incorrectly reported as S24NE4

The ALSA sink reports both S24NE4 (sample in LSB) and 24-bit S32NE
(sample in MSB) as AE_FMT_S24NE4.

Report the latter correctly as AE_FMT_S24NE4MSB instead, otherwise
sample conversion goes wrong resulting in noise.

Addresses http://forum.xbmc.org/showthread.php?tid=203120