uwb: use time_after() when purging stale beacons

void uwb_beca_purge(void)

{

	struct uwb_beca_e *bce, *next;

	unsigned long now = jiffies;

	unsigned long expires;

	mutex_lock(&uwb_beca.mutex);

	list_for_each_entry_safe(bce, next, &uwb_beca.list, node) {

		if (now - bce->ts_jiffies

		    > msecs_to_jiffies(beacon_timeout_ms)) {

		expires = bce->ts_jiffies + msecs_to_jiffies(beacon_timeout_ms);

		if (time_after(jiffies, expires)) {

			uwbd_dev_offair(bce);

			list_del(&bce->node);

			uwb_bce_put(bce);