PCI/MSI: Remove pci_msi_domain_{alloc,free}_irqs()

Just call the msi_* version directly instead of having trivial wrappers for
one or two callsites.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>