usb: wwan: fix compilation without CONFIG_PM_RUNTIME

The pm usage counter must be accessed with the proper wrappers
to allow compilation under all configurations.
Signed-off-by: Oliver Neukum <oneukum@suse.de>
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/usb_wwan.c

@@ -698,8 +698,7 @@ static void play_delayed(struct usb_serial_port *port)
 			/* we have to throw away the rest */
 			do {
 				unbusy_queued_urb(urb, portdata);
-				//extremely dirty
-				atomic_dec(&port->serial->interface->dev.power.usage_count);
+				usb_autopm_put_interface_no_suspend(port->serial->interface);
 			} while ((urb = usb_get_from_anchor(&portdata->delayed)));
 			break;
 		}