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/rt73usb.c b/drivers/net/wireless/rt2x00/rt73usb.c
index dc640bf..c0671c2 100644
--- a/drivers/net/wireless/rt2x00/rt73usb.c
+++ b/drivers/net/wireless/rt2x00/rt73usb.c
@@ -1251,7 +1251,7 @@
 }
 
 static int rt73usb_get_tx_data_len(struct rt2x00_dev *rt2x00dev,
-				   int maxpacket, struct sk_buff *skb)
+				   struct sk_buff *skb)
 {
 	int length;
 
@@ -1260,7 +1260,7 @@
 	 * but it must _not_ be a multiple of the USB packet size.
 	 */
 	length = roundup(skb->len, 4);
-	length += (4 * !(length % maxpacket));
+	length += (4 * !(length % rt2x00dev->usb_maxpacket));
 
 	return length;
 }