abx500-chargalg: Add new sysfs interface to get current charge status

Allow a user to check on AB8500 charging status from debugfs.

Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/power/ab8500_charger.c

@@ -2764,6 +2764,9 @@ static int ab8500_charger_usb_notifier_call(struct notifier_block *nb,
 	enum ab8500_usb_state bm_usb_state;
 	unsigned mA = *((unsigned *)power);
 
+	if (!di)
+		return NOTIFY_DONE;
+
 	if (event != USB_EVENT_VBUS) {
 		dev_dbg(di->dev, "not a standard host, returning\n");
 		return NOTIFY_DONE;