device: Load the current finger print and not always the first print

In the garbage collection code we always ended up to load the first
enrolled print, and this may lead to removing from device storage prints
that are actually in use.

src/device.c

@@ -1471,7 +1471,7 @@ try_delete_print (FprintDevice *rdev)
           guint index;
 
           store.print_data_load (priv->dev,
-                                 GPOINTER_TO_UINT (fingers->data),
+                                 GPOINTER_TO_UINT (finger->data),
                                  username,
                                  &print);