device-info-cache: use Log.warning instead of Log.critical

Log.critical does not actually exist.
When logging error, it will in fact throw an exception:

[string "device-info-cache.lua"]:36: attempt to call a nil value
(field 'critical')

Change Log.critical to Log.warning to fix it.

src/scripts/lib/device-info-cache.lua

@@ -33,7 +33,7 @@ function module.get_device_info (self, device)
   if not dev_info then
     local device_name = device_properties ["device.name"]
     if not device_name then
-      Log.critical (device, "invalid device.name")
+      Log.warning (device, "invalid device.name")
       return nil
     end