vdpa/ifcvf: fix the calculation of queuepair

The q_pair_id to address a queue pair in the lm bar should be
calculated by queue_id / 2 rather than queue_id / nr_vring.

Fixes: 2ddae773c93b ("vDPA/ifcvf: detect and use the onboard number of queues directly")
Signed-off-by: Angus Chen <[e-mail]>
Reviewed-by: Jason Wang <[e-mail]>
Reviewed-by: Michael S. Tsirkin <[e-mail]>
Acked-by: Zhu Lingshan <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>

drivers/vdpa/ifcvf/ifcvf_base.c

···
 	u32 q_pair_id;
 
 	ifcvf_lm = (struct ifcvf_lm_cfg __iomem *)hw->lm_cfg;
-	q_pair_id = qid / hw->nr_vring;
+	q_pair_id = qid / 2;
 	avail_idx_addr = &ifcvf_lm->vring_lm_cfg[q_pair_id].idx_addr[qid % 2];
 	last_avail_idx = vp_ioread16(avail_idx_addr);
 
···
 	u32 q_pair_id;
 
 	ifcvf_lm = (struct ifcvf_lm_cfg __iomem *)hw->lm_cfg;
-	q_pair_id = qid / hw->nr_vring;
+	q_pair_id = qid / 2;
 	avail_idx_addr = &ifcvf_lm->vring_lm_cfg[q_pair_id].idx_addr[qid % 2];
 	hw->vring[qid].last_avail_idx = num;
 	vp_iowrite16(num, avail_idx_addr);