[media] tw686x: Don't go past array

Depending on the compiler version, currently it produces the
following warnings:
	tw686x-video.c: In function 'tw686x_video_init':
	tw686x-video.c:65:543: warning: array subscript is above array bounds [-Warray-bounds]

This is actually bogus with the current code, as it currently
hardcodes the framerate to 30 frames/sec, however a potential
use after the array size could happen when the driver adds support
for setting the framerate. So, fix it.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/pci/tw686x/tw686x-video.c

@@ -61,8 +61,17 @@ static unsigned int tw686x_fields_map(v4l2_std_id std, unsigned int fps)
 		   8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 0, 0
 	};
 
-	unsigned int i =
-		(std & V4L2_STD_625_50) ? std_625_50[fps] : std_525_60[fps];
+	unsigned int i;
+
+	if (std & V4L2_STD_525_60) {
+		if (fps > ARRAY_SIZE(std_525_60))
+			fps = 30;
+		i = std_525_60[fps];
+	} else {
+		if (fps > ARRAY_SIZE(std_625_50))
+			fps = 25;
+		i = std_625_50[fps];
+	}
 
 	return map[i];
 }