Xen: use qemu_strtoul instead of strtol

No need to roll our own (with slightly incorrect handling of errno),
when we can use the common version.

Change signed parsing to unsigned, because what it read are values in
PCI config space, which are non-negative.
Signed-off-by: NCao jin <caoj.fnst@cn.fujitsu.com>
Reviewed-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

hw/xen/xen-host-pci-device.c

@@ -141,7 +141,7 @@ static int xen_host_pci_get_value(XenHostPCIDevice *d, const char *name,
     char buf[XEN_HOST_PCI_GET_VALUE_BUFFER_SIZE];
     int fd, rc;
     unsigned long value;
-    char *endptr;
+    const char *endptr;
 
     xen_host_pci_sysfs_path(d, name, path, sizeof(path));
 
@@ -158,13 +158,9 @@ static int xen_host_pci_get_value(XenHostPCIDevice *d, const char *name,
         }
     } while (rc < 0);
     buf[rc] = 0;
-    value = strtol(buf, &endptr, base);
-    if (endptr == buf || *endptr != '\n') {
-        rc = -1;
-    } else if ((value == LONG_MIN || value == LONG_MAX) && errno == ERANGE) {
-        rc = -errno;
-    } else {
-        rc = 0;
+    rc = qemu_strtoul(buf, &endptr, base, &value);
+    if (!rc) {
+        assert(value <= UINT_MAX);
         *pvalue = value;
     }
 out: