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.com


Signed-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>