can: sja1000: fix use after free in ems_pcmcia_add_card()

If the last channel is not available then "dev" is freed.  Fortunately,
we can just use "pdev->irq" instead.

Also we should check if at least one channel was set up.

Fixes: fd734c6f ("can/sja1000: add driver for EMS PCMCIA card")
Link: https://lore.kernel.org/all/20211124145041.GB13656@kili
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/sja1000/ems_pcmcia.c

@@ -234,7 +234,12 @@ static int ems_pcmcia_add_card(struct pcmcia_device *pdev, unsigned long base)
 			free_sja1000dev(dev);
 	}
 
-	err = request_irq(dev->irq, &ems_pcmcia_interrupt, IRQF_SHARED,
+	if (!card->channels) {
+		err = -ENODEV;
+		goto failure_cleanup;
+	}
+
+	err = request_irq(pdev->irq, &ems_pcmcia_interrupt, IRQF_SHARED,
 			  DRV_NAME, card);
 	if (!err)
 		return 0;