confile_utils: cleanup sig_parse()

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

src/lxc/confile_utils.c

@@ -1039,5 +1039,5 @@ int sig_parse(const char *signame)
 				return signames[n].num;
 	}
 
-	return -1;
+	return ret_errno(EINVAL);
 }