cxacru: treat firmware data as const

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/drivers/usb/atm/cxacru.c b/drivers/usb/atm/cxacru.c
index 5ea3093..90583d6 100644
--- a/drivers/usb/atm/cxacru.c
+++ b/drivers/usb/atm/cxacru.c
@@ -820,7 +820,7 @@
 }
 
 static int cxacru_fw(struct usb_device *usb_dev, enum cxacru_fw_request fw,
-		     u8 code1, u8 code2, u32 addr, u8 *data, int size)
+		     u8 code1, u8 code2, u32 addr, const u8 *data, int size)
 {
 	int ret;
 	u8 *buf;