xend: pci: find_parent: should return string rather than int

Using changeset 19783: 61ec78692b13, device assignment can't work:
e.g., in find_the_uppermost_pci_bridge(),
 parent = dev_parent.find_parent()
...
 dev_parent = PciDevice(parent),
we can see parent['domain'] is int and in PciDevice's __init__,
int(dev['domain'], 16) would fail:
TypeError: int() can't convert non-string with explicit base

Signed-off-by: Dexuan Cui <dexuan.cui@intel.com>

tools/python/xen/util/pci.py

@@ -547,12 +547,12 @@ class PciDevice:
             else:
                 dev = {}
                 lst = parent.split(':')
-                dev['domain'] = int(lst[0], 16)
-                dev['bus'] = int(lst[1], 16)
+                dev['domain'] = '%04x' % int(lst[0], 16)
+                dev['bus'] = '%02x' % int(lst[1], 16)
                 lst = lst[2]
                 lst = lst.split('.')
-                dev['slot'] = int(lst[0], 16)
-                dev['func'] = int(lst[1], 16)
+                dev['slot'] = '%02x' % int(lst[0], 16)
+                dev['func'] = '%x' % int(lst[1], 16)
             return dev
         except OSError, (errno, strerr):
             raise PciDeviceParseError('Can not locate the parent of %s',