checkpatch: add check for reuse of krealloc arg

On Thu, 2013-03-14 at 13:30 +0000, David Woodhouse wrote:
> If krealloc() returns NULL, it *doesn't* free the original. So any code
> of the form 'foo = krealloc(foo, …);' is almost certainly a bug.

So add a check for it to checkpatch.

Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>