dvb frontends: treat firmware data as const

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/drivers/media/dvb/frontends/nxt200x.c b/drivers/media/dvb/frontends/nxt200x.c
index 23d0228..af29835 100644
--- a/drivers/media/dvb/frontends/nxt200x.c
+++ b/drivers/media/dvb/frontends/nxt200x.c
@@ -93,7 +93,8 @@
 	return 0;
 }
 
-static int nxt200x_writebytes (struct nxt200x_state* state, u8 reg, u8 *buf, u8 len)
+static int nxt200x_writebytes (struct nxt200x_state* state, u8 reg,
+			       const u8 *buf, u8 len)
 {
 	u8 buf2 [len+1];
 	int err;