esp: Simplify the calculation of variables

Fix the following coccicheck warnings:

./net/ipv6/esp6.c:791:16-18: WARNING !A || A && B is equivalent
to !A || B.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv6/esp6.c

@@ -793,7 +793,7 @@ int esp6_input_done2(struct sk_buff *skb, int err)
 	int hlen = sizeof(struct ip_esp_hdr) + crypto_aead_ivsize(aead);
 	int hdr_len = skb_network_header_len(skb);
 
-	if (!xo || (xo && !(xo->flags & CRYPTO_DONE)))
+	if (!xo || !(xo->flags & CRYPTO_DONE))
 		kfree(ESP_SKB_CB(skb)->tmp);
 
 	if (unlikely(err))