ALSA: au88x0: remove redundant assignment of variable i

The assignment to variable i is redundant as it is never read
because it is updated a little later on. Remove this assignment.
Cleans up clang warning: Value stored to 'i' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>