storaged: skip batteryproperties listener if uid_io not available

uid_monitor is the only user of batteryproperties, no need to register
a callback if uid_io not enabled.

Test: run storaged without uid_io, plug/unplug usb cable
Merged-In: If890a93fec155b67c450341c54b44bb18d3aae3d
Change-Id: If890a93fec155b67c450341c54b44bb18d3aae3d
diff --git a/storaged/storaged.cpp b/storaged/storaged.cpp
index 72bb6e2..1770922 100644
--- a/storaged/storaged.cpp
+++ b/storaged/storaged.cpp
@@ -170,6 +170,9 @@
 }
 
 void storaged_t::init_battery_service() {
+    if (!mConfig.proc_uid_io_available)
+        return;
+
     sp<IBatteryPropertiesRegistrar> battery_properties = get_battery_properties_service();
     if (battery_properties == NULL) {
         LOG_TO(SYSTEM, WARNING) << "failed to find batteryproperties service";