HID: playstation: fix unused variable in ps_battery_get_property.

The ret variable in ps_battery_get_property is set in an error path,
but never actually returned. Change the function to return ret.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Roderick Colenbrander <roderick.colenbrander@sony.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>