RDMA/hns: Correct the value of HNS_ROCE_HEM_CHUNK_LEN

Size of pointer to buf field of struct hns_roce_hem_chunk should be
considered when calculating HNS_ROCE_HEM_CHUNK_LEN, or sg table size will
be larger than expected when allocating hem.

Fixes: 9a44353 ("IB/hns: Add driver files for hns RoCE driver")
Link: https://lore.kernel.org/r/1572575610-52530-2-git-send-email-liweihang@hisilicon.com
Signed-off-by: Sirong Wang <wangsirong@huawei.com>
Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hns/hns_roce_hem.h

@@ -59,7 +59,7 @@ enum {
 
 #define HNS_ROCE_HEM_CHUNK_LEN	\
 	 ((256 - sizeof(struct list_head) - 2 * sizeof(int)) /	 \
-	 (sizeof(struct scatterlist)))
+	 (sizeof(struct scatterlist) + sizeof(void *)))
 
 #define check_whether_bt_num_3(type, hop_num) \
 	(type < HEM_TYPE_MTT && hop_num == 2)