[PATCH] libata: refuse to register IRQless ports

We don't currently support pure polled operation so when we meet a BIOS
which forgot to assign an IRQ to a PCI device it all goes a little pear
shaped. Trap this case properly.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>