V4L/DVB (4743): Fix oops in VIDIOC_G_PARM

The call to v4l2_std_construct() in the VIDIOC_G_PARM handler treats
vfd->current_norm as if it were an index - but it's not.  The result is
an oops if the driver has no vidioc_g_parm() method defined.  Here's the
fix.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/videodev.c

@@ -1288,6 +1288,7 @@ static int __video_do_ioctl(struct inode *inode, struct file *file,
 			ret=vfd->vidioc_g_parm(file, fh, p);
 		} else {
 			struct v4l2_standard s;
+			int i;
 
 			if (!vfd->tvnormsize) {
 				printk (KERN_WARNING "%s: no TV norms defined!\n",
@@ -1298,8 +1299,14 @@ static int __video_do_ioctl(struct inode *inode, struct file *file,
 			if (p->type != V4L2_BUF_TYPE_VIDEO_CAPTURE)
 				return -EINVAL;
 
-			v4l2_video_std_construct(&s, vfd->tvnorms[vfd->current_norm].id,
-						 vfd->tvnorms[vfd->current_norm].name);
+			for (i = 0; i < vfd->tvnormsize; i++)
+				if (vfd->tvnorms[i].id == vfd->current_norm)
+					break;
+			if (i >= vfd->tvnormsize)
+				return -EINVAL;
+
+			v4l2_video_std_construct(&s, vfd->current_norm,
+						 vfd->tvnorms[i].name);
 
 			memset(p,0,sizeof(*p));