ALSA: doc: Fix spelling mistakes

correct Reatek to Realtek

Signed-off-by: huangjianghui <huangjianghui@uniontech.com>
Link: https://lore.kernel.org/r/20210610062036.30300-1-huangjianghui@uniontech.com


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