No attempt has been made to document any of the demoted structs here.

Fixes the following W=1 kernel build warning(s):

 drivers/iio/adc/max9611.c:117: warning: cannot understand function prototype: 'const unsigned int max9611_mux_conf[][2] = '
 drivers/iio/adc/max9611.c:145: warning: cannot understand function prototype: 'const unsigned int max9611_gain_conf[][2] = '

Cc: Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>