rt2x00: add driver private field to struct rt2x00_dev

Enhance rt2x00 infrastructure by adding driver specific field to
struct rt2x00_dev.

The new field will be used by rt2800 drivers for chipset registers
access abstraction layer.
Signed-off-by: NBartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Acked-by: NIvo van Doorn <IvDoorn@gmail.com>
Acked-by: NGertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00.h

@@ -842,6 +842,11 @@ struct rt2x00_dev {
 	 * Firmware image.
 	 */
 	const struct firmware *fw;
+
+	/*
+	 * Driver specific data.
+	 */
+	void *priv;
 };
 
 /*