Documentation/vm/slabinfo.c: clean up this code

This patch does the following cleanups for Documentation/vm/slabinfo.c:

	- Fix two memory leaks;
	- Constify some char pointers;
	- Use snprintf instead of sprintf in case of buffer overflow;
	- Fix some indentations;
	- Other little improvements.

Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>