[PATCH] Fix oops in video_register_device

[PATCH] Fix oops in video_register_device

degerrit@web.de wrote:
   "I caused an oops in unusual circumstances by accidentally "forcing" a
    video device number which was too high or already taken (don't know
    which). I assume this probably shouldn't give an oops (though it was my
     fault), so here's a bugreport..."

Fixed by adding a range check for the number passed in by the driver.