iwl3945: use iwl_tx_cmd_complete

iwl3945 uses iwl_tx_cmd_complete to reclaim the unused buffers of the queue.
iwl_tx_cmd_complete in turn call the iwl_hcmd_queue_reclaim which will
unmap the dma mapping to tx_cmd and frees the memory.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>