auxdisplay: img-ascii-lcd: add missing sentinel entry in img_ascii_lcd_matches

The OF device table must be terminated, otherwise we'll be walking past it
and into areas unknown.

Fixes: 0cad855f

 ("auxdisplay: img-ascii-lcd: driver for simple ASCII...")
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>