V4L: check inval in video_register_device_index()

From: Henrik Kretzschmar <[email protected]>

Better check the video_device pointer before using it.

index 6f36006..ef153ff 100644
@@ -257,6 +257,9 @@ int video_register_device_index(struct video_device *vfd, int type, int nr,

	int ret;
	char *name_base;

+ if (vfd == NULL)
+ return -EINVAL;
+

	switch (type) {
	case VFL_TYPE_GRABBER:
		base = MINOR_VFL_TYPE_GRABBER_MIN;