uio: don't free irq that was not requested

UIO base driver should only free_irq that it has requested.
UIO supports drivers without interrupts (irq == 0) or custom handlers.

This fixes warnings like:

WARNING: CPU: 1 PID: 5478 at kernel/irq/manage.c:1244 __free_irq+0xa9/0x1e0()
Trying to free already-free IRQ 0
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uio/uio.c

@@ -879,7 +879,8 @@ void uio_unregister_device(struct uio_info *info)
 
 	uio_dev_del_attributes(idev);
 
-	free_irq(idev->info->irq, idev);
+	if (info->irq && info->irq != UIO_IRQ_CUSTOM)
+		free_irq(info->irq, idev);
 
 	device_destroy(&uio_class, MKDEV(uio_major, idev->minor));