propogate the error if resolve_external_mounts() fails

collect_mnt_namespaces() returns with ret=0 if resolve_external_mounts()
fails.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -2677,7 +2677,8 @@ int collect_mnt_namespaces(bool for_dump)
 	if (ret)
 		goto err;
 
-	if (resolve_external_mounts(mntinfo))
+	ret = resolve_external_mounts(mntinfo);
+	if (ret)
 		goto err;
 
 	if (arg.need_to_validate) {