hwmon: (ina3221) Demote seemingly unintentional kerneldoc header

hwmon: (ina3221) Demote seemingly unintentional kerneldoc header

This is the only use of kerneldoc in the sourcefile and no
descriptions are provided.

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

 drivers/hwmon/ina3221.c:152: warning: Function parameter or member 'ina' not described in 'ina3221_summation_shunt_resistor'

Cc: "Andrew F. Davis" <afd@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112095715.1993117-3-lee.jones@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>