net: dsa: tag_hellcreek: Cleanup includes

Remove unused and add needed includes. No functional change.
Suggested-by: NVladimir Oltean <olteanv@gmail.com>
Signed-off-by: NKurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Reviewed-by: NVladimir Oltean <olteanv@gmail.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>

net/dsa/tag_hellcreek.c

@@ -8,9 +8,7 @@
  * Based on tag_ksz.c.
  */
 
-#include <linux/etherdevice.h>
-#include <linux/list.h>
-#include <linux/slab.h>
+#include <linux/skbuff.h>
 #include <net/dsa.h>
 
 #include "dsa_priv.h"