s390/ism: Fix trying to free already-freed IRQ by repeated ism_dev_exit()

This patch prevents the system from crashing when unloading the ISM module.

How to reproduce: Attach an ISM device and execute 'rmmod ism'.

Error-Log:
- Trying to free already-free IRQ 0
- WARNING: CPU: 1 PID: 966 at kernel/irq/manage.c:1890 free_irq+0x140/0x540

After calling ism_dev_exit() for each ISM device in the exit routine,
pci_unregister_driver() will execute ism_remove() for each ISM device.
Because ism_remove() also calls ism_dev_exit(),
free_irq(pci_irq_vector(pdev, 0), ism) is called twice for each ISM
device. This results in a crash with the error
'Trying to free already-free IRQ'.

In the exit routine, it is enough to call pci_unregister_driver()
because it ensures that ism_dev_exit() is called once per
ISM device.

Cc: <stable@vger.kernel.org> # 6.3+
Fixes: 89e7d2b ("net/ism: Add new API for client registration")
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Julian Ruess <julianr@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: juru1234

drivers/s390/net/ism_drv.c

@@ -771,14 +771,6 @@ static int __init ism_init(void)
 
 static void __exit ism_exit(void)
 {
-	struct ism_dev *ism;
-
-	mutex_lock(&ism_dev_list.mutex);
-	list_for_each_entry(ism, &ism_dev_list.list, list) {
-		ism_dev_exit(ism);
-	}
-	mutex_unlock(&ism_dev_list.mutex);
-
 	pci_unregister_driver(&ism_driver);
 	debug_unregister(ism_debug_info);
 }