[ath] Add missing break statements

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/ath/ath5k/ath5k_desc.c

 		case AR5K_PKT_TYPE_BEACON:
 		case AR5K_PKT_TYPE_PROBE_RESP:
 			frame_type = AR5K_AR5210_TX_DESC_FRAME_TYPE_NO_DELAY;
+			break;
 		case AR5K_PKT_TYPE_PIFS:
 			frame_type = AR5K_AR5210_TX_DESC_FRAME_TYPE_PIFS;
+			break;
 		default:
 			frame_type = type /*<< 2 ?*/;
+			break;
 		}
 
 		tx_ctl->tx_control_0 |=