ALSA: emu10k1: introduce and use snd_emu10k1_ptr_write_multiple()

While this nicely denoises the code, the real intent is being able to
write many registers pseudo-atomically, which will come in handy later.

Idea stolen from kX-project.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

Link: https://lore.kernel.org/r/20230518093134.3697955-1-oswald.buddenhagen@gmx.de


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