Modification and bug fixes with respect to irq registration.

- Enable interrupts after request_irq

- Restored MSI data register value at driver unload time
Signed-off-by: Ananda Raju <ananda.raju@neterion.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>