rt2x00: Fix sparse warning on nested container_of()

Sparse produces warnings about nested contain_of() statements,
this means that lines like:
	interface_to_usbdev(to_usb_interface(rt2x00dev->dev));
will upset sparse.
Add a new macro to rt2x00usb.h which will convert to device
structure to the usb_device pointer in 2 steps to prevent this
sparse warning.
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2500usb.c

@@ -1672,8 +1672,7 @@ static int rt2500usb_probe_hw(struct rt2x00_dev *rt2x00dev)
 static int rt2500usb_beacon_update(struct ieee80211_hw *hw, struct sk_buff *skb)
 {
 	struct rt2x00_dev *rt2x00dev = hw->priv;
-	struct usb_device *usb_dev =
-		interface_to_usbdev(to_usb_interface(rt2x00dev->dev));
+	struct usb_device *usb_dev = to_usb_device_intf(rt2x00dev->dev);
 	struct ieee80211_tx_info *tx_info = IEEE80211_SKB_CB(skb);
 	struct rt2x00_intf *intf = vif_to_intf(tx_info->control.vif);
 	struct queue_entry_priv_usb_bcn *bcn_priv;

drivers/net/wireless/rt2x00/rt2x00usb.c

@@ -40,8 +40,7 @@ int rt2x00usb_vendor_request(struct rt2x00_dev *rt2x00dev,
 			     void *buffer, const u16 buffer_length,
 			     const int timeout)
 {
-	struct usb_device *usb_dev =
-		interface_to_usbdev(to_usb_interface(rt2x00dev->dev));
+	struct usb_device *usb_dev = to_usb_device_intf(rt2x00dev->dev);
 	int status;
 	unsigned int i;
 	unsigned int pipe =
@@ -162,8 +161,7 @@ static void rt2x00usb_interrupt_txdone(struct urb *urb)
 int rt2x00usb_write_tx_data(struct queue_entry *entry)
 {
 	struct rt2x00_dev *rt2x00dev = entry->queue->rt2x00dev;
-	struct usb_device *usb_dev =
-		interface_to_usbdev(to_usb_interface(rt2x00dev->dev));
+	struct usb_device *usb_dev = to_usb_device_intf(rt2x00dev->dev);
 	struct queue_entry_priv_usb *entry_priv = entry->priv_data;
 	struct skb_frame_desc *skbdesc;
 	u32 length;
@@ -319,8 +317,7 @@ EXPORT_SYMBOL_GPL(rt2x00usb_disable_radio);
 void rt2x00usb_init_rxentry(struct rt2x00_dev *rt2x00dev,
 			    struct queue_entry *entry)
 {
-	struct usb_device *usb_dev =
-		interface_to_usbdev(to_usb_interface(rt2x00dev->dev));
+	struct usb_device *usb_dev = to_usb_device_intf(rt2x00dev->dev);
 	struct queue_entry_priv_usb *entry_priv = entry->priv_data;
 
 	usb_fill_bulk_urb(entry_priv->urb, usb_dev,

drivers/net/wireless/rt2x00/rt2x00usb.h

@@ -26,6 +26,12 @@
 #ifndef RT2X00USB_H
 #define RT2X00USB_H
 
+#define to_usb_device_intf(d) \
+({ \
+	struct usb_interface *intf = to_usb_interface(d); \
+	interface_to_usbdev(intf); \
+})
+
 /*
  * This variable should be used with the
  * usb_driver structure initialization.