Documentation: sound: fix typo in control-names.rst

change 'cannel' to 'channel'

Signed-off-by: Sunrisepeak <speakshen@163.com>
Link: https://lore.kernel.org/r/20220227145204.16600-1-speakshen@163.com


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