hwmon: (twl4030-madc-hwmon) Initialize uninitialized structure elements

twl4030_madc_conversion uses do_avg and type structure elements of
twl4030_madc_request. Initialize structure to avoid random operation.

Fix for: Coverity CID 200794 Uninitialized scalar variable.

Cc: Keerthy <j-keerthy@ti.com>
Cc: stable@vger.kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Keerthy <j-keerthy@ti.com>