usage.c: remove reference to busybox.h
*: s/include "busybox.h"/include "libbb.h"

diff --git a/util-linux/mkswap.c b/util-linux/mkswap.c
index a84792c..88f1fbb 100644
--- a/util-linux/mkswap.c
+++ b/util-linux/mkswap.c
@@ -6,7 +6,7 @@
  * Licensed under GPL version 2, see file LICENSE in this tarball for details.
  */
 
-#include "busybox.h"
+#include "libbb.h"
 
 int mkswap_main(int argc, char **argv);
 int mkswap_main(int argc, char **argv)