ACPI: battery: Drop redundant test for failure

Merging the two adjacent conditionally built blocks makes the code
a lot more readable.  And as a bonus, we drop a duplicate test when
CONFIG_ACPI_PROCFS_POWER is undefined.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>