[IPV6]: Make fib6_node subtree depend on IPV6_SUBTREES

Make fib6_node 'subtree' depend on IPV6_SUBTREES.

Signed-off-by: Kim Nordlund <kim.nordlund@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 9f80518..8c3d568 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -494,7 +494,7 @@
 				goto out; \
 			pn = fn->parent; \
 			if (FIB6_SUBTREE(pn) && FIB6_SUBTREE(pn) != fn) \
-				fn = fib6_lookup(pn->subtree, NULL, saddr); \
+				fn = fib6_lookup(FIB6_SUBTREE(pn), NULL, saddr); \
 			else \
 				fn = pn; \
 			if (fn->fn_flags & RTN_RTINFO) \