passthrough/PCI: replace improper uses of pci_find_next_cap()

Using pci_find_next_cap() without prior pci_find_cap_offset() is bogus
(and possibly wrong, given that the latter doesn't check the
PCI_STATUS_CAP_LIST flag, which so far was checked in an open-coded way
only for the non-bridge case).

Once at it, fold the two calls into one, as we need its result in any
case.

Question is whether, without any caller left, pci_find_next_cap()
should be purged as well.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -589,16 +589,13 @@ void pci_release_devices(struct domain *
 
 int pdev_type(u16 seg, u8 bus, u8 devfn)
 {
-    u16 class_device;
-    u16 status, creg;
-    int pos;
+    u16 class_device, creg;
     u8 d = PCI_SLOT(devfn), f = PCI_FUNC(devfn);
+    int pos = pci_find_cap_offset(seg, bus, d, f, PCI_CAP_ID_EXP);
 
     class_device = pci_conf_read16(seg, bus, d, f, PCI_CLASS_DEVICE);
     if ( class_device == PCI_CLASS_BRIDGE_PCI )
     {
-        pos = pci_find_next_cap(seg, bus, devfn,
-                                PCI_CAPABILITY_LIST, PCI_CAP_ID_EXP);
         if ( !pos )
             return DEV_TYPE_LEGACY_PCI_BRIDGE;
         creg = pci_conf_read16(seg, bus, d, f, pos + PCI_EXP_FLAGS);
@@ -606,15 +603,7 @@ int pdev_type(u16 seg, u8 bus, u8 devfn)
             DEV_TYPE_PCIe2PCI_BRIDGE : DEV_TYPE_PCIe_BRIDGE;
     }
 
-    status = pci_conf_read16(seg, bus, d, f, PCI_STATUS);
-    if ( !(status & PCI_STATUS_CAP_LIST) )
-        return DEV_TYPE_PCI;
-
-    if ( pci_find_next_cap(seg, bus, devfn, PCI_CAPABILITY_LIST,
-                           PCI_CAP_ID_EXP) )
-        return DEV_TYPE_PCIe_ENDPOINT;
-
-    return DEV_TYPE_PCI;
+    return pos ? DEV_TYPE_PCIe_ENDPOINT : DEV_TYPE_PCI;
 }
 
 /*