power: supply: bq256xx: add kerneldoc for structure members

Document members of structure to fix W=1 warnings like:

  drivers/power/supply/bq256xx_charger.c:240: warning:
    Function parameter or member 'charger' not described in 'bq256xx_device'
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/bq256xx_charger.c

@@ -202,6 +202,8 @@ enum bq256xx_id {
  * @client: i2c client structure
  * @regmap: register map structure
  * @dev: device structure
+ * @charger: power supply registered for the charger
+ * @battery: power supply registered for the battery
  * @lock: mutex lock structure
  *
  * @usb2_phy: usb_phy identifier