hwmon: (acpi_power_meter) Fix a check for the return value of read_domain_devices().

After commit fabb1f8 ("hwmon: (acpi_power_meter) Fix fail to load
module on platform without _PMD method"),
the acpi_power_meter driver fails to load if the platform has _PMD method.

To address this, add a check for successful read_domain_devices().
Tested on Nvidia Grace machine.

Fixes: fabb1f8 ("hwmon: (acpi_power_meter) Fix fail to load module on platform without _PMD method")
Signed-off-by: Kazuhiro Abe <fj1078ii@aa.jp.fujitsu.com>
Link: https://lore.kernel.org/r/20250115073532.3211000-1-fj1078ii@aa.jp.fujitsu.com
[groeck: Dropped unnecessary () from expression]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: Kazuhiro-Abe-fj

drivers/hwmon/acpi_power_meter.c

@@ -682,7 +682,7 @@ static int setup_attrs(struct acpi_power_meter_resource *resource)
 
 	/* _PMD method is optional. */
 	res = read_domain_devices(resource);
-	if (res != -ENODEV)
+	if (res && res != -ENODEV)
 		return res;
 
 	if (resource->caps.flags & POWER_METER_CAN_MEASURE) {