xen/pci: Used cached MSI-X capability offset

We now cache the MSI-X capability offset in the struct pci_dev, so no
need to find the capability again.
Acked-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/pci/xen.c

@@ -295,8 +295,7 @@ static int xen_initdom_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 			int pos;
 			u32 table_offset, bir;
 
-			pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
-
+			pos = dev->msix_cap;
 			pci_read_config_dword(dev, pos + PCI_MSIX_TABLE,
 					      &table_offset);
 			bir = (u8)(table_offset & PCI_MSIX_TABLE_BIR);