ASoC: pcm1681: remove useless assignment

cppcheck warning:

sound/soc/codecs/pcm1681.c:87:8: style: Variable 'i' is assigned a
value that is never used. [unreadVariable]
 int i = 0, val = -1, enable = 0;
       ^

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210312182246.5153-17-pierre-louis.bossart@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>