[media] cx25821: off by one in cx25821_vidioc_s_input()

If "i" is 2 then when we call cx25821_video_mux() we'd end up going
past the end of the cx25821_boards[dev->board]->input[].

The INPUT() macro obfuscates what's going on in that function so it's
a bit hard to follow.  And as Mauro points out the hard coded 2 is
not very helpful.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/cx25821/cx25821-video.c

@@ -1312,7 +1312,7 @@ int cx25821_vidioc_s_input(struct file *file, void *priv, unsigned int i)
 			return err;
 	}
 
-	if (i > 2) {
+	if (i >= CX25821_NR_INPUT) {
 		dprintk(1, "%s(): -EINVAL\n", __func__);
 		return -EINVAL;
 	}

drivers/media/video/cx25821/cx25821.h

@@ -98,6 +98,7 @@
 #define CX25821_BOARD_CONEXANT_ATHENA10 1
 #define MAX_VID_CHANNEL_NUM     12
 #define VID_CHANNEL_NUM 8
+#define CX25821_NR_INPUT 2
 
 struct cx25821_fmt {
 	char *name;
@@ -196,7 +197,7 @@ struct cx25821_board {
 	unsigned char radio_addr;
 
 	u32 clk_freq;
-	struct cx25821_input input[2];
+	struct cx25821_input input[CX25821_NR_INPUT];
 };
 
 struct cx25821_subid {