ACPI: battery: Fix CONFIG_ACPI_SYSFS_POWER=n

Disabling CONFIG_ACPI_SYSFS_POWER changes the behaviour of
acpi_battery_update().  It will call acpi_battery_get_info()
even if the battery is not present.  I haven't noticed this
causing any problem, but it does look like a bad idea.

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Acked-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>