scsi: target: cxgbit: Fix cxgbit_fw4_ack()

Use the pointer 'p' after having tested that pointer instead of before.

Fixes: 5cadafb ("target/cxgbit: Fix endianness annotations")
Cc: Varun Prakash <varun@chelsio.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20191023202150.22173-1-bvanassche@acm.org
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/iscsi/cxgbit/cxgbit_cm.c

@@ -1829,7 +1829,7 @@ static void cxgbit_fw4_ack(struct cxgbit_sock *csk, struct sk_buff *skb)
 
 	while (credits) {
 		struct sk_buff *p = cxgbit_sock_peek_wr(csk);
-		const u32 csum = (__force u32)p->csum;
+		u32 csum;
 
 		if (unlikely(!p)) {
 			pr_err("csk 0x%p,%u, cr %u,%u+%u, empty.\n",
@@ -1838,6 +1838,7 @@ static void cxgbit_fw4_ack(struct cxgbit_sock *csk, struct sk_buff *skb)
 			break;
 		}
 
+		csum = (__force u32)p->csum;
 		if (unlikely(credits < csum)) {
 			pr_warn("csk 0x%p,%u, cr %u,%u+%u, < %u.\n",
 				csk,  csk->tid,