da9030_battery: Don't use 0 as NULL

Noticed the new warning:

  CHECK   drivers/power/da9030_battery.c
drivers/power/da9030_battery.c:190:68: warning: Using plain integer as NULL pointer

This commit fixes the issue.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
1 file changed