power: supply: qcom_pmi8998_charger: fix uninitialized variable

smatch warnings:
  drivers/power/supply/qcom_pmi8998_charger.c:565 smb2_status_change_work() error: uninitialized symbol 'usb_online'.

usb_online is used uninitialized whenever smb2_get_prop_usb_online()
returns a negative value.

Thus, fix the issue by initializing usb_online to 0.

Fixes: 8648aeb5 ("power: supply: add Qualcomm PMI8998 SMB2 Charger driver")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/r/202307280638.556PrzIS-lkp@intel.com/Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org
Link: https://lore.kernel.org/r/20230802023130.2516232-1-liaoyu15@huawei.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/qcom_pmi8998_charger.c

@@ -556,7 +556,8 @@ static int smb2_set_current_limit(struct smb2_chip *chip, unsigned int val)
 static void smb2_status_change_work(struct work_struct *work)
 {
 	unsigned int charger_type, current_ua;
-	int usb_online, count, rc;
+	int usb_online = 0;
+	int count, rc;
 	struct smb2_chip *chip;
 
 	chip = container_of(work, struct smb2_chip, status_change_work.work);