Staging: asus_oled: fix image processing

Programming an image was broken, because odev->buf_offs was not advanced
for val == 0 in append_values(). This regression was introduced in:

 commit 1ff12a4a
 Author: Kevin A. Granade <kevin.granade@gmail.com>
 Date:   Sat Sep 5 01:03:39 2009 -0500

     Staging: asus_oled: Cleaned up checkpatch issues.

Fix the image processing by special-casing val == 0.

I have tested this change on an Asus G50V laptop only.

Cc: Jakub Schmidtke <sjakub@gmail.com>
Cc: Kevin A. Granade <kevin.granade@gmail.com>
Signed-off-by: Pekka Paalanen <pq@iki.fi>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>