eeepc-wmi: include slab.h

eeepc-wmi uses kfree() but doesn't include slab.h.  Include it.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Yong Wang <yong.y.wang@intel.com>

drivers/platform/x86/eeepc-wmi.c

@@ -27,6 +27,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/types.h>
+#include <linux/slab.h>
 #include <linux/input.h>
 #include <linux/input/sparse-keymap.h>
 #include <acpi/acpi_bus.h>