scsi: megaraid_sas: fix error handle in megasas_probe_one

megasas_mgmt_info.max_index has increased by 1 before megasas_io_attach,
if megasas_io_attach return error, then goto fail_io_attach,
megasas_mgmt_info.instance has a wrong index here. So first reduce
max_index and then set that instance to NULL.
Signed-off-by: Nweiping zhang <zhangweiping@didichuxing.com>
Acked-by: NSumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/megaraid/megaraid_sas_base.c

@@ -6228,8 +6228,8 @@ static int megasas_probe_one(struct pci_dev *pdev,
 fail_start_aen:
 fail_io_attach:
 	megasas_mgmt_info.count--;
-	megasas_mgmt_info.instance[megasas_mgmt_info.max_index] = NULL;
 	megasas_mgmt_info.max_index--;
+	megasas_mgmt_info.instance[megasas_mgmt_info.max_index] = NULL;
 
 	instance->instancet->disable_intr(instance);
 	megasas_destroy_irqs(instance);