ALSA: emu10k1: enable bit-exact playback, part 3: pitch

ALSA: emu10k1: enable bit-exact playback, part 3: pitch

CPF_CURRENTPITCH starts swerving towards PTRX_PITCHTARGET as soon as
that is set. In practice this means that CPF_FRACADDRESS may acquire a
non-zero value before we manage to force CPF_CURRENTPITCH to the final
value, which would prevent bit-for-bit reproduction.

To avoid that this state persists, we now reset CPF_FRACADDRESS when
setting CPF_CURRENTPITCH, and to (mostly) avoid that it progresses too
far in the first place (possibly even reaching CCCA_CURRADDR), we write
PTRX and CPF in one critical section (though NMIs, etc. still make this
unreliable).

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230518140339.3722279-2-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>