rt2x00: Move TX descriptor field "ifs" into plcp substruct

"ifs" is only used by no-HT devices. Move it into the plcp substruct and
fill in the value only for no-HT devices.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
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/rt2500usb.c b/drivers/net/wireless/rt2x00/rt2500usb.c
index ed5bc9c..979fe65 100644
--- a/drivers/net/wireless/rt2x00/rt2500usb.c
+++ b/drivers/net/wireless/rt2x00/rt2500usb.c
@@ -1100,7 +1100,7 @@
 			   (txdesc->rate_mode == RATE_MODE_OFDM));
 	rt2x00_set_field32(&word, TXD_W0_NEW_SEQ,
 			   test_bit(ENTRY_TXD_FIRST_FRAGMENT, &txdesc->flags));
-	rt2x00_set_field32(&word, TXD_W0_IFS, txdesc->ifs);
+	rt2x00_set_field32(&word, TXD_W0_IFS, txdesc->u.plcp.ifs);
 	rt2x00_set_field32(&word, TXD_W0_DATABYTE_COUNT, txdesc->length);
 	rt2x00_set_field32(&word, TXD_W0_CIPHER, !!txdesc->cipher);
 	rt2x00_set_field32(&word, TXD_W0_KEY_ID, txdesc->key_idx);