bin: fix deep-element-added signal debug log message

Adding the bin to the child element doesn't really make sense.
diff --git a/gst/gstbin.c b/gst/gstbin.c
index 3719c40..e575aee 100644
--- a/gst/gstbin.c
+++ b/gst/gstbin.c
@@ -1459,7 +1459,7 @@
 
   GST_LOG_OBJECT (parent_bin, "emitting deep-element-added for element "
       "%" GST_PTR_FORMAT " which has just been added to %" GST_PTR_FORMAT,
-      sub_bin, child);
+      child, sub_bin);
 
   g_signal_emit (parent_bin, gst_bin_signals[DEEP_ELEMENT_ADDED], 0, sub_bin,
       child);