power-status: Use correct DBus signatures

Devices are represented as susdut, not susbut (i.e. the percentage
is a double rather than a boolean) - apparently the wrong signature
works, but correct it anyway.

https://bugzilla.gnome.org/show_bug.cgi?id=660122

js/ui/status/power.js

@@ -43,8 +43,8 @@ const UPDeviceState = {
 const PowerManagerInterface = {
     name: 'org.gnome.SettingsDaemon.Power',
     methods: [
-        { name: 'GetDevices', inSignature: '', outSignature: 'a(susbut)' },
-        { name: 'GetPrimaryDevice', inSignature: '', outSignature: '(susbut)' },
+        { name: 'GetDevices', inSignature: '', outSignature: 'a(susdut)' },
+        { name: 'GetPrimaryDevice', inSignature: '', outSignature: '(susdut)' },
         ],
     signals: [
         { name: 'Changed', inSignature: '' },