scsi: hisi_sas: Relocate call to hisi_sas_debugfs_exit()

Currently we call function hisi_sas_debugfs_exit() to remove debugfs_dir
before freeing interrupt irqs and destroying workqueue in the driver remove
path.

If a dump is triggered before function hisi_sas_debugfs_exit() but
debugfs_work may be called after it, so it may refer to already removed
debugfs_dir which will cause NULL pointer dereference.

To avoid it, put function hisi_sas_debugfs_exit() after free_irqs and
destroy workqueue when removing hisi_sas driver.

Link: https://lore.kernel.org/r/1573551059-107873-4-git-send-email-john.garry@huawei.comSigned-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_v3_hw.c

@@ -3302,8 +3302,6 @@ static void hisi_sas_v3_remove(struct pci_dev *pdev)
 	struct hisi_hba *hisi_hba = sha->lldd_ha;
 	struct Scsi_Host *shost = sha->core.shost;
 
-	hisi_sas_debugfs_exit(hisi_hba);
-
 	if (timer_pending(&hisi_hba->timer))
 		del_timer(&hisi_hba->timer);
 
@@ -3315,6 +3313,7 @@ static void hisi_sas_v3_remove(struct pci_dev *pdev)
 	pci_release_regions(pdev);
 	pci_disable_device(pdev);
 	hisi_sas_free(hisi_hba);
+	hisi_sas_debugfs_exit(hisi_hba);
 	scsi_host_put(shost);
 }