PCI: fix ats compile failure

I get this compile failure on parisc:

drivers/pci/ats.c: In function 'ats_alloc_one':
drivers/pci/ats.c:29: error: implicit declaration of function 'kzalloc'
drivers/pci/ats.c:29: warning: assignment makes pointer from integer without a cast
drivers/pci/ats.c: In function 'ats_free_one':
drivers/pci/ats.c:45: error: implicit declaration of function 'kfree'

Because ats.c is missing linux/slab.h as an include.  This patch fixes it
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/ats.c

@@ -13,6 +13,7 @@
 #include <linux/export.h>
 #include <linux/pci-ats.h>
 #include <linux/pci.h>
+#include <linux/slab.h>
 
 #include "pci.h"