modules/mtree: Do not log an error when prefix not found.

A not found prefix is already represented as a negative return code.
No need to log an error, as it may be perfectly valid that a prefix does not
exists.

modules/mtree/mtree_mod.c

@@ -445,7 +445,7 @@ again:
 
 	if(mt_match_prefix(msg, tr, &tomatch, mval)<0)
 	{
-		LM_INFO("no prefix found in [%.*s] for [%.*s]\n",
+		LM_DBG("no prefix found in [%.*s] for [%.*s]\n",
 				tname.len, tname.s,
 				tomatch.len, tomatch.s);
 		goto error;