power: supply: bq256xx: Handle OOM correctly

Since we now return a pointer to an allocated object we need
to account for memory allocation failure in a separate
error path.

Fixes: 25fd3303

 ("power: supply_core: Pass pointer to battery info")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>