Update header includes.

src/data_source.c

@@ -7,9 +7,9 @@
 #include <assert.h>
 #include <stdlib.h>
 
+#include <libburn.h>
+#include <libisofs.h>
 #include "isoburn.h"
-#include "../libisofs/libisofs.h"
-#include "../libburn/libburn.h"
 
 struct disc_data_src {
  struct burn_drive *d;