scsi: qla4xxx: switch to pci_alloc_irq_vectors

And simplify the MSI-X logic in general - just request the two vectors
directly instead of going through an indirection table.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nilesh Javali <nilesh.javali@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>