ath9k: fix dma direction for map/unmap in ath_rx_tasklet

For edma, we should use DMA_BIDIRECTIONAL, or else use
DMA_FROM_DEVICE.

This is found to address "BUG at arch/x86/mm/physaddr.c:5"
as described here:

http://lkml.org/lkml/2010/7/14/21Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/recv.c

@@ -844,9 +844,9 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush, bool hp)
 	int dma_type;
 
 	if (edma)
-		dma_type = DMA_FROM_DEVICE;
-	else
 		dma_type = DMA_BIDIRECTIONAL;
+	else
+		dma_type = DMA_FROM_DEVICE;
 
 	qtype = hp ? ATH9K_RX_QUEUE_HP : ATH9K_RX_QUEUE_LP;
 	spin_lock_bh(&sc->rx.rxbuflock);