xfrm6: release dev before returning error

We forget to call dev_put() on error path in xfrm6_fill_dst(),
its caller doesn't handle this.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: NCong Wang <amwang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/xfrm6_policy.c

@@ -103,8 +103,10 @@ static int xfrm6_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
 	dev_hold(dev);
 
 	xdst->u.rt6.rt6i_idev = in6_dev_get(dev);
-	if (!xdst->u.rt6.rt6i_idev)
+	if (!xdst->u.rt6.rt6i_idev) {
+		dev_put(dev);
 		return -ENODEV;
+	}
 
 	rt6_transfer_peer(&xdst->u.rt6, rt);