tcp_memcontrol: fix reversed if condition

We should only dereference the pointer if it's valid, not the other way
round.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_memcontrol.c

@@ -44,7 +44,7 @@ static inline struct tcp_memcontrol *tcp_from_cgproto(struct cg_proto *cg_proto)
 
 static void memcg_tcp_enter_memory_pressure(struct sock *sk)
 {
-	if (!sk->sk_cgrp->memory_pressure)
+	if (sk->sk_cgrp->memory_pressure)
 		*sk->sk_cgrp->memory_pressure = 1;
 }
 EXPORT_SYMBOL(memcg_tcp_enter_memory_pressure);