PCI/MSI: Fix cut-and-paste errors in documentation

Function pci_enable_msi_range() is used in examples where
pci_enable_msix_range() should have been used instead.

Reported-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>