net/xen-netfront: Correct printf format in xennet_get_responses

rx->status is an int16_t, print it using %d rather than %u in order to
have a meaningful value when the field is negative.

Also use %u rather than %x for rx->offset.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>