usb-host-libusb: Configuration 0 may be a valid configuration

Quoting from: linux/Documentation/ABI/stable/sysfs-bus-usb:

	Note that some devices, in violation of the USB spec, have a
	configuration with a value equal to 0. Writing 0 to
	bConfigurationValue for these devices will install that
	configuration, rather then unconfigure the device.

So don't compare the configuration value against 0 to check for unconfigured
devices, instead check for a LIBUSB_ERROR_NOT_FOUND return from
libusb_get_active_config_descriptor().
Signed-off-by: NHans de Goede <hdegoede@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/host-libusb.c

@@ -992,15 +992,14 @@ static int usb_host_claim_interfaces(USBHostDevice *s, int configuration)
     udev->ninterfaces   = 0;
     udev->configuration = 0;
 
-    if (configuration == 0) {
-        /* address state - ignore */
-        return USB_RET_SUCCESS;
-    }
-
     usb_host_detach_kernel(s);
 
     rc = libusb_get_active_config_descriptor(s->dev, &conf);
     if (rc != 0) {
+        if (rc == LIBUSB_ERROR_NOT_FOUND) {
+            /* address state - ignore */
+            return USB_RET_SUCCESS;
+        }
         return USB_RET_STALL;
     }