nvme/pci: Remove last_cq_head

We had been saving the last_cq_head seen from an interrupt so that a
polled queue wouldn't mistakenly trigger spruious interrupt detection. We
don't poll interrupt driven queues any more, so saving this value is
pointless.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NKeith Busch <kbusch@kernel.org>

drivers/nvme/host/pci.c

@@ -176,7 +176,6 @@ struct nvme_queue {
 	u16 sq_tail;
 	u16 last_sq_tail;
 	u16 cq_head;
-	u16 last_cq_head;
 	u16 qid;
 	u8 cq_phase;
 	u8 sqes;
@@ -1026,10 +1025,7 @@ static irqreturn_t nvme_irq(int irq, void *data)
 	 * the irq handler, even if that was on another CPU.
 	 */
 	rmb();
-	if (nvmeq->cq_head != nvmeq->last_cq_head)
-		ret = IRQ_HANDLED;
 	nvme_process_cq(nvmeq, &start, &end, -1);
-	nvmeq->last_cq_head = nvmeq->cq_head;
 	wmb();
 
 	if (start != end) {