[stable] mtdchar: fix offset overflow detection

[Luis Henriques]

On Mon, Apr 15, 2013 at 01:27:10AM +0100, Ben Hutchings wrote:
> Brad Spengler pointed out this fix from 3.6 was missing from the earlier
> stable branches:
> 
> commit 9c603e53d380459fb62fec7cd085acb0b74ac18f
> Author: Linus Torvalds <torvalds at linux-foundation.org>
> Date:   Sat Sep 8 12:57:30 2012 -0700
> 
>     mtdchar: fix offset overflow detection
> 
> It looks cleanly cherry-pickable, although I haven't yet tested this.

Thanks, I'll queue it for 3.5 as well.

Cheers,
--
Luis