ahci: fix the single MSI-X case in ahci_init_one

We need to make sure hpriv->irq is set properly if we don't use per-port
vectors, so switch from blindly assigning pdev->irq to using
pci_irq_vector, which handles all interrupt types correctly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Robert Richter <robert.richter@cavium.com>
Tested-by: Robert Richter <robert.richter@cavium.com>
Tested-by: David Daney <ddaney.cavm@gmail.com>
Fixes: 0b9e2988

 ("ahci: use pci_alloc_irq_vectors")
Signed-off-by: Tejun Heo <tj@kernel.org>