rt2x00: rt2800: fix zeroing skb structure

We should clear skb->data not skb itself. Bug was introduced by:
commit 0b8004aa12d13ec750d102ba4082a95f0107c649 "rt2x00: Properly
reserve room for descriptors in skbs".

Cc: stable@kernel.org # 2.6.36+
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -703,8 +703,7 @@ void rt2800_write_beacon(struct queue_entry *entry, struct txentry_desc *txdesc)
 	/*
 	 * Add space for the TXWI in front of the skb.
 	 */
-	skb_push(entry->skb, TXWI_DESC_SIZE);
-	memset(entry->skb, 0, TXWI_DESC_SIZE);
+	memset(skb_push(entry->skb, TXWI_DESC_SIZE), 0, TXWI_DESC_SIZE);
 
 	/*
 	 * Register descriptor details in skb frame descriptor.