pcmcia: fix 'driver ... did not release config properly' warning

Up to 2.6.34 pcmcia_release_irq() reset p_dev->_irq to 0 after releasing
the irq.  The IRQ is now released in pcmcia_disable_device(), however
p_dev->_irq is not reset, triggering a warning in pcmcia_device_remove().

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>