power: supply: cpcap-charger: Fix null check for power_supply_get_by_name

In the cpcap_usb_detect() function, the power_supply_get_by_name()
function may return `NULL` instead of an error pointer.
To prevent potential null pointer dereferences, Added a null check.

Fixes: eab4e6d ("power: supply: cpcap-charger: get the battery inserted infomation from cpcap-battery")
Signed-off-by: Charles Han <hanchunchao@inspur.com>
Link: https://lore.kernel.org/r/20250519024741.5846-1-hanchunchao@inspur.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: Charles Han

drivers/power/supply/cpcap-charger.c

@@ -689,9 +689,8 @@ static void cpcap_usb_detect(struct work_struct *work)
 		struct power_supply *battery;
 
 		battery = power_supply_get_by_name("battery");
-		if (IS_ERR_OR_NULL(battery)) {
-			dev_err(ddata->dev, "battery power_supply not available %li\n",
-					PTR_ERR(battery));
+		if (!battery) {
+			dev_err(ddata->dev, "battery power_supply not available\n");
 			return;
 		}