[DECNET]: net/decnet/dn_route.c: fix inconsequent NULL checking

The Coverity checker noted this inconsequent NULL checking in
dnrt_drop().

Since all callers ensure that NULL isn't passed, we can simply remove
the check.
Signed-off-by: NAdrian Bunk <bunk@stusta.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/decnet/dn_route.c

@@ -149,8 +149,7 @@ static inline void dnrt_free(struct dn_route *rt)
 
 static inline void dnrt_drop(struct dn_route *rt)
 {
-	if (rt)
-		dst_release(&rt->u.dst);
+	dst_release(&rt->u.dst);
 	call_rcu_bh(&rt->u.dst.rcu_head, dst_rcu_free);
 }