tcp_memcontrol: remove a redundant statement in tcp_destroy_cgroup()

We read the value but make no use of it.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_memcontrol.c

@@ -72,8 +72,6 @@ void tcp_destroy_cgroup(struct mem_cgroup *memcg)
 
 	tcp = tcp_from_cgproto(cg_proto);
 	percpu_counter_destroy(&tcp->tcp_sockets_allocated);
-
-	val = res_counter_read_u64(&tcp->tcp_memory_allocated, RES_LIMIT);
 }
 EXPORT_SYMBOL(tcp_destroy_cgroup);