hwmon: (acpi_power_meter) Fix build warning

Commit c5dec018

 (acpi_power_meter: Use struct
dev_pm_ops for power management) introduced the following build warning. It is
seen if CONFIG_PM_SLEEP is not defined.

acpi_power_meter.c:930:12: warning: acpi_power_meter_resume defined but not used

Fix it.

Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>