dsound: change mix rate of primary buffer

[sebastien chev]

It seems that no matter what the Windows side program choose for
DirectSoundCreate, the DSound subsystem initialize itself with the higher
spec sound available (for example 48Khz Float32, or 48kHz Int16 if no
Float32 available).

While not a big deal on current linux PC, using this on ARM device kill
performance.

A DirectSound subsystem for ARM, with Integer only for the mixbuffer (as
most ARM still use softfloat) and 22kHz should be less taxing for
performances.