Corrects BQ256XX_NUM_WD_VAL from value of "8" to "4" and fixes the issue when 'i'
is equal to array size then array index over runs the array

Fixes: 32e4978b ("power: supply: bq256xx: Introduce the BQ256XX charger driver")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Ricardo Rivera-Matos <r-rivera-matos@ti.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>