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>