at86rf230: assign wait_for_completion_timeout to appropriately typed var

return type of wait_for_completion_timeout is unsigned long not int.
As rc is used here only for wait_for_completion_timeout the type is simply
changed to unsigned long.
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/net/ieee802154/at86rf230.c

@@ -689,7 +689,7 @@ at86rf230_sync_state_change_complete(void *context)
 static int
 at86rf230_sync_state_change(struct at86rf230_local *lp, unsigned int state)
 {
-	int rc;
+	unsigned long rc;
 
 	at86rf230_async_state_change(lp, &lp->state, state,
 				     at86rf230_sync_state_change_complete,