ASoC: max9867: make array ni_div static const

The array ni_div does not need to be in global scope and is not
modified, so make it static const.

Cleans up sparse warning:
"symbol 'ni_div' was not declared. Should it be static?"

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-By: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>