rt2x00: fix rt2x00usb_regbusy_read() arguments

Add const to 'field' argument of rt2x00usb_regbusy_read()
(all arguments match rt2x00pci_regbusy_read() ones now).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800usb.h

@@ -44,7 +44,7 @@ struct rt2800_ops {
 
 	int (*regbusy_read)(struct rt2x00_dev *rt2x00dev,
 			    const unsigned int offset,
-			    struct rt2x00_field32 field, u32 *reg);
+			    const struct rt2x00_field32 field, u32 *reg);
 };
 
 static inline void rt2800_register_read(struct rt2x00_dev *rt2x00dev,

drivers/net/wireless/rt2x00/rt2x00usb.c

@@ -156,7 +156,7 @@ EXPORT_SYMBOL_GPL(rt2x00usb_vendor_request_large_buff);
 
 int rt2x00usb_regbusy_read(struct rt2x00_dev *rt2x00dev,
 			   const unsigned int offset,
-			   struct rt2x00_field32 field,
+			   const struct rt2x00_field32 field,
 			   u32 *reg)
 {
 	unsigned int i;

drivers/net/wireless/rt2x00/rt2x00usb.h

@@ -365,7 +365,7 @@ static inline void rt2x00usb_register_multiwrite(struct rt2x00_dev *rt2x00dev,
  */
 int rt2x00usb_regbusy_read(struct rt2x00_dev *rt2x00dev,
 			   const unsigned int offset,
-			   struct rt2x00_field32 field,
+			   const struct rt2x00_field32 field,
 			   u32 *reg);
 
 /*