iwlwifi: clear rxq->queue in queue reset

In iwl_rx_queue_reset(), we didn't clear the rxq->queue[]. This might
cause the same rxb appears on multiple places in rxq->queue. Although
this won't cause any problem because of the read and write pointers
protection in rxq, we'd better clear it to avoid misleading.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>