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

After commit fabb1f81 ("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: fabb1f81 ("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>