ALSA: emu10k1: merge common paths in snd_emu10k1_ptr_{read,write}()

Avoids some code duplication.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230514170323.3408798-3-oswald.buddenhagen@gmx.de


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