rt2x00: Reverse calling order of bus write_tx_desc and driver write_tx_desc.

For rt2800 reverse the calling order of rt2x00pci_write_data and
rt2800pci_write_data. Currently rt2800pci_write_data calls rt2x00pci_write_data
as there can be only 1 driver callback function specified by the driver.
Reverse this calling order by introducing a new driver callback function,
called write_tx_datadesc, which is called from the bus-specific write_tx_data
functions.
Preparation for futher cleanups in the skb data handling of rt2x00.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
diff --git a/drivers/net/wireless/rt2x00/rt2x00usb.c b/drivers/net/wireless/rt2x00/rt2x00usb.c
index bd1546b..25cc376 100644
--- a/drivers/net/wireless/rt2x00/rt2x00usb.c
+++ b/drivers/net/wireless/rt2x00/rt2x00usb.c
@@ -248,6 +248,12 @@
 	 */
 	skb_pull(entry->skb, entry->queue->desc_size);
 
+	/*
+	 * Call the driver's write_tx_datadesc function, if it exists.
+	 */
+	if (rt2x00dev->ops->lib->write_tx_datadesc)
+		rt2x00dev->ops->lib->write_tx_datadesc(entry, txdesc);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(rt2x00usb_write_tx_data);