Add missing include statements

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

--- a/drivers/net/wireless/ath9k/regd.c
+++ b/drivers/net/wireless/ath9k/regd.c
@@ -14,6 +14,8 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <linux/kernel.h>
+#include <linux/slab.h>
 #include "ath9k.h"
 #include "regd.h"
 #include "regd_common.h"