udev: only report a warning if udev_enumerate_scan_devices fails

Even if an error is reported by `udev_enumerate_scan_devices`,
e.g. because a driver of a device has an bug, we can still enumerate
all other devices. Additionally the documentation of
udev_enumerate_scan_devices says that on success an integer >= 0 is
returned (see man udev_enumerate_scan_devices(3)).
Reviewed-by: NBjoern Walk <bwalk@linux.ibm.com>
Signed-off-by: NMarc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/node_device/node_device_udev.c

@@ -1480,13 +1480,8 @@ udevEnumerateDevices(struct udev *udev)
     if (udevEnumerateAddMatches(udev_enumerate) < 0)
         goto cleanup;
 
-    ret = udev_enumerate_scan_devices(udev_enumerate);
-    if (ret != 0) {
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("udev scan devices returned %d"),
-                       ret);
-        goto cleanup;
-    }
+    if (udev_enumerate_scan_devices(udev_enumerate) < 0)
+        VIR_WARN("udev scan devices failed");
 
     udev_list_entry_foreach(list_entry,
                             udev_enumerate_get_list_entry(udev_enumerate)) {
@@ -1494,6 +1489,7 @@ udevEnumerateDevices(struct udev *udev)
         udevProcessDeviceListEntry(udev, list_entry);
     }
 
+    ret = 0;
  cleanup:
     udev_enumerate_unref(udev_enumerate);
     return ret;