Both the kernel and criu uses unsigned int
for it, make the format appropriate.

	| struct mount_info {
	|	...
	|	unsigned int		s_dev;
	|	...
	| }

We didn't see negative number here in real life so
I don't think if such %d to %u convention cause
backward compatibility problem ever.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>