scsi: csiostor: switch to pci_alloc_irq_vectors

And get automatic MSI-X affinity for free.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>