drm/ttm: using kmalloc/kfree requires including slab.h

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_page_alloc.c

@@ -37,6 +37,7 @@
 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/seq_file.h> /* for seq_printf */
+#include <linux/slab.h>
 
 #include <asm/atomic.h>
 #include <asm/agp.h>