usb: musb: cppi41: fix condition to call cppi41_trans_done().

connect AR9271(USB wifi) to AM335x, and send a flood ping from Mac OSX,
AR9271 is stopped.

on USB bus, the following occurs.

 - OUT transaction is ACKed (NYET).
 - IN transaction is ACKed (512bytes).
 - PING-NAK transaction is continued for about 2 seconds (AR9271 timeout?).

In current imprementation, IN-transaction is not completed because it
checks the empty of TX-FIFO in cppi41_dma_callback().
As a result, communication to AR9271 stops.

This patch modified to check the empty of TX-FIFO only when OUT-transaction.
Signed-off-by: Takeyoshi Kikuchi <kikuchi@centurysys.co.jp>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_cppi41.c

@@ -250,8 +250,10 @@ static void cppi41_dma_callback(void *private_data)
 			transferred < cppi41_channel->packet_sz)
 		cppi41_channel->prog_len = 0;
 
+	if (cppi41_channel->is_tx)
 		empty = musb_is_tx_fifo_empty(hw_ep);
-	if (empty) {
+
+	if (!cppi41_channel->is_tx || empty) {
 		cppi41_trans_done(cppi41_channel);
 		goto out;
 	}