ALSA: emu10k1: don't limit multi-channel playback to two periods

ALSA: emu10k1: don't limit multi-channel playback to two periods

For unclear reasons, the extra voice was set up with half the buffer
size instead of the period size. Commit 27ae958cf6 ("emu10k1 driver -
add multichannel device hw:x,3 [2-8/8]") mentions half-loop interrupts,
so maybe this was an artifact of an earlier iteration of the patch.

While at it, also fix periods_min of the regular playback - one period
makes just no sense.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230523200709.236023-2-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>