V4L/DVB (13954): Correct NULL test

Test the just-allocated value for NULL rather than some other value.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r@
identifier f;
@@

f(...) { <+... return NULL; ...+> }

@@
expression *x;
expression y;
identifier r.f;
statement S;
@@

x = f(...);
(
if ((x) == NULL) S
|
if (
-   y
+   x
       == NULL)
 S
)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/usbvision/usbvision-video.c

@@ -1487,7 +1487,7 @@ static int __devinit usbvision_register_video(struct usb_usbvision *usbvision)
 		usbvision->vbi = usbvision_vdev_init(usbvision,
 						     &usbvision_vbi_template,
 						     "USBVision VBI");
-		if (usbvision->vdev == NULL) {
+		if (usbvision->vbi == NULL) {
 			goto err_exit;
 		}
 		if (video_register_device(usbvision->vbi,