ALSA: emu10k1: refactor PCM playback cache filling

Rename snd_emu10k1_playback_invalidate_cache() to the more apt
snd_emu10k1_playback_fill_cache(), and factor out
snd_emu10k1_playback_prepare_voices(), which calls the former for all
channels.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230517174256.3657060-8-oswald.buddenhagen@gmx.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>