rt2x00: Request usb_maxpacket() once

The usb max packet size won't change during the
device's presence. We should store it in a
variable inside rt2x00dev and use that.
This should also fix a division error when the
device is being hot-unplugged while a frame is
being send out.

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/rt2x00.h b/drivers/net/wireless/rt2x00/rt2x00.h
index d1ad525..c8f16f1 100644
--- a/drivers/net/wireless/rt2x00/rt2x00.h
+++ b/drivers/net/wireless/rt2x00/rt2x00.h
@@ -418,7 +418,7 @@
 	int (*write_tx_data) (struct rt2x00_dev *rt2x00dev,
 			      struct data_ring *ring, struct sk_buff *skb,
 			      struct ieee80211_tx_control *control);
-	int (*get_tx_data_len) (struct rt2x00_dev *rt2x00dev, int maxpacket,
+	int (*get_tx_data_len) (struct rt2x00_dev *rt2x00dev,
 				struct sk_buff *skb);
 	void (*kick_tx_queue) (struct rt2x00_dev *rt2x00dev,
 			       unsigned int queue);
@@ -599,6 +599,11 @@
 	u32 *rf;
 
 	/*
+	 * USB Max frame size (for rt2500usb & rt73usb).
+	 */
+	u16 usb_maxpacket;
+
+	/*
 	 * Current TX power value.
 	 */
 	u16 tx_power;