pcmcia: avoid buffer overflow in pcmcia_setup_isa_irq

NR_IRQS may be as low as 16, causing a (harmless?) buffer overflow in
pcmcia_setup_isa_irq():

static u8 pcmcia_used_irq[NR_IRQS];

...

		if ((try < 32) && pcmcia_used_irq[irq])
			continue;

This is read-only, so if this address would be non-zero, it would just
mean we would not attempt an IRQ >= NR_IRQS -- which would fail anyway!
And as request_irq() fails for an irq >= NR_IRQS, the setting code path:

			pcmcia_used_irq[irq]++;

is never reached as well.

Reported-by: Christoph Fritz <chf.fritz@googlemail.com>
CC: stable@kernel.org
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>

drivers/pcmcia/pcmcia_resource.c

@@ -677,7 +677,7 @@ EXPORT_SYMBOL(__pcmcia_request_exclusive_irq);
 #ifdef CONFIG_PCMCIA_PROBE
 
 /* mask of IRQs already reserved by other cards, we should avoid using them */
-static u8 pcmcia_used_irq[NR_IRQS];
+static u8 pcmcia_used_irq[32];
 
 static irqreturn_t test_action(int cpl, void *dev_id)
 {
@@ -700,6 +700,9 @@ static int pcmcia_setup_isa_irq(struct pcmcia_device *p_dev, int type)
 	for (try = 0; try < 64; try++) {
 		irq = try % 32;
 
+		if (irq > NR_IRQS)
+			continue;
+
 		/* marked as available by driver, not blocked by userspace? */
 		if (!((mask >> irq) & 1))
 			continue;