rt2x00: Re-order tx descriptor writing code in drivers.

Where possible, write the tx descriptor words from start to end, to
follow a logical ordering of words.
Where this is not possible (in rt2400pci, rt2500pci and rt61pci) add
a comment as to why word 0 needs to be written last.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rt2x00/rt61pci.c b/drivers/net/wireless/rt2x00/rt61pci.c
index 99c2981..55aa010 100644
--- a/drivers/net/wireless/rt2x00/rt61pci.c
+++ b/drivers/net/wireless/rt2x00/rt61pci.c
@@ -1813,6 +1813,11 @@
 		rt2x00_desc_write(txd, 11, word);
 	}
 
+	/*
+	 * Writing TXD word 0 must the last to prevent a race condition with
+	 * the device, whereby the device may take hold of the TXD before we
+	 * finished updating it.
+	 */
 	rt2x00_desc_read(txd, 0, &word);
 	rt2x00_set_field32(&word, TXD_W0_OWNER_NIC, 1);
 	rt2x00_set_field32(&word, TXD_W0_VALID, 1);