[media] s5h1420: fix a buffer overflow when checking userspace params

The maximum size for a DiSEqC command is 6, according to the
userspace API. However, the code allows to write up to 7 values:
	drivers/media/dvb-frontends/s5h1420.c:193 s5h1420_send_master_cmd() error: buffer overflow 'cmd->msg' 6 <= 7

Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/dvb-frontends/s5h1420.c

@@ -180,7 +180,7 @@ static int s5h1420_send_master_cmd (struct dvb_frontend* fe,
 	int result = 0;
 
 	dprintk("enter %s\n", __func__);
-	if (cmd->msg_len > 8)
+	if (cmd->msg_len > sizeof(cmd->msg))
 		return -EINVAL;
 
 	/* setup for DISEQC */