Decompressors: include <linux/slab.h> in <linux/decompress/mm.h>

Decompressors: include <linux/slab.h> in <linux/decompress/mm.h>

Currently users of mm.h need to include <linux/slab.h> to use the macros
malloc() and free() provided by mm.h.  This fixes it.

Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alain Knaff <alain@knaff.lu>
Cc: Albin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: Phillip Lougher <phillip@lougher.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>