libata: update gfp/slab.h includes

Implicit slab.h inclusion via percpu.h is about to go away.  Make sure
gfp.h or slab.h is included as necessary.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Jeff Garzik <jgarzik@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci_platform.c

@@ -13,6 +13,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/gfp.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>

drivers/ata/libahci.c

@@ -33,6 +33,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/gfp.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/blkdev.h>