rt2x00: Fix TX short preamble detection

The short preamble mode was not correctly detected during TX,
rt2x00 used the rate->hw_value_short field but mac80211 is not
using this field that way.
Instead the flag IEEE80211_TX_RC_USE_SHORT_PREAMBLE should be
used to determine if the frame should be send out using
short preamble or not.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rt2x00/rt2x00queue.c b/drivers/net/wireless/rt2x00/rt2x00queue.c
index eaec6bd..746a8f3 100644
--- a/drivers/net/wireless/rt2x00/rt2x00queue.c
+++ b/drivers/net/wireless/rt2x00/rt2x00queue.c
@@ -313,7 +313,7 @@
 		 * When preamble is enabled we should set the
 		 * preamble bit for the signal.
 		 */
-		if (rt2x00_get_rate_preamble(rate->hw_value))
+		if (rate->flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE)
 			txdesc->signal |= 0x08;
 	}
 }